Communities and Conversation Glossary · UGC Platforms

2023 blackout: the June 12, 2023 protest in which thousands of Reddit communities (over 7,800 by one count) went private or restricted posting over Data API pricing, showing that moderators control availability and their tools are infrastructure (Volunteer Moderation & Community Governance).
Abandonment: a community whose owner and moderators have stopped moderating and is drifting into spam; the platform hands it to an active member (checked against the owner's recent activity, with notice to the owner) or closes it (Communities, Roles & Permissions).
ActivityPub: the W3C Recommendation (since January 23, 2018) behind Mastodon, the wider fediverse and Threads' opt-in federation, in which servers deliver activities such as Create, Follow and Delete to each other's inboxes by HTTP POST (Federation & Open Protocols).
Actor: in ActivityPub, a user, group or service with an inbox and an outbox; posting adds an activity to the outbox and federation delivers it to recipients' inboxes (Federation & Open Protocols).
Adjacency list: thread storage where each comment points at its parent and a subtree is read with a recursive query; paired with a materialized path, it's the default here (Posts, Comments & Voting).
ADMINISTRATOR: the Discord permission bit that grants every permission and skips channel overwrites entirely (Communities, Roles & Permissions).
AI answer: an answer a model composes from retrieved community threads, shown only with citations to the items it drew on and held to search's filters, so a removal of any cited item invalidates every cached answer citing it (Search & Discovery).
Answer-ness: a search ranking signal that favors, for question-shaped queries, threads with accepted or highly voted answers over threads with only the question (Search & Discovery).
API pricing: charging developers for API access; Reddit's terms effective July 1, 2023 kept free limits per OAuth client and charged $0.24 per 1,000 calls above them, with moderation tools exempted (Developer Platforms, APIs & Data Access).
AppView: an AT Protocol service that indexes the network from the firehose and serves the aggregated views apps need: threads, like and repost counts, follower lists, search (Federation & Open Protocols).
Archiving: closing old threads to new comments and votes after a period, which caps the surface spammers and manipulators can reach and lets scores freeze (Posts, Comments & Voting).
AT Protocol: Bluesky's protocol, which separates where a user's data lives (a PDS) from the relays, AppViews, feed generators and labelers that index, rank and moderate it (Federation & Open Protocols).
Automation share: the share of moderator actions made by automated tools; 68.6% of Reddit moderators' removals in the second half of 2025 were automated (Volunteer Moderation & Community Governance).
Automod: a rules engine that volunteer moderators configure to remove, hold or report posts and comments matching conditions on the item and its author's account; it should offer structured rules first, linear-time regular expressions second, hard limits, a report-only mode and attribution of every action to its rule (Volunteer Moderation & Community Governance).
AutoMod (Discord): Discord's structured automod with published limits per server: six keyword rules (up to 1,000 keywords and 10 regular expressions each) and one each for spam, keyword presets, mention spam and member profiles, with block, alert, timeout and block-interactions actions (Volunteer Moderation & Community Governance).
AutoModerator: Reddit's per-community rules engine, configured by moderators, that removes, holds or reports items matching conditions on the item and on its author's account, such as account age and reputation (Volunteer Moderation & Community Governance).
Base permissions: the first step of the permission algorithm: the default role's permissions ORed with those of every role the member holds (Communities, Roles & Permissions).
Block: a one-way filter that hides each account from the other everywhere (feeds, replies, search, mentions, recommendations, chat), enforced in every service in both directions (Feeds & Recommendations).
Blocklist (federation): a list of domain blocks shared between fediverse admins as a CSV file; it cuts off bad servers fast but propagates errors as fast, so imports should record their source and be reviewed (Federation & Open Protocols).
Bot sharding: splitting a bot's gateway connections across shards, which Discord requires from 2,500 servers, assigning each server by shard_id = (guild_id >> 22) % num_shards (Real-Time Chat).
Bridgy Fed: a bridge between ActivityPub, the AT Protocol and the web, opt-in per user: bridging is off until the user enables it and off again when they block it (Federation & Open Protocols).
Brigading: members of one community descending on another to vote or comment, answered with links that don't allow voting from the referral and tools that show moderators where a surge came from (Posts, Comments & Voting).
Bucket: a time window (about ten days in Discord's design) that, combined with the channel id, forms a message partition key so no partition grows past a comfortable size (Real-Time Chat).
Candidate generation: the first recommendation stage, in which several sources (the viewer's graph, similar users, embedding neighbors, related and trending items) each cheaply propose hundreds to thousands of items (Feeds & Recommendations).
Category: a channel that holds other channels and carries permission overwrites they can inherit (Communities, Roles & Permissions).
Category sync: a channel following its category's overwrites, so changing the category changes every synced channel; editing the child's own overwrites breaks the sync (Communities, Roles & Permissions).
Channel: a conversation space inside a community with its own audience, kind (text, forum, announcement, voice, stage, category) and permission overwrites (Communities, Roles & Permissions).
Channel (streaming): one person's community on a streaming platform: the broadcaster owns it, appoints moderators and VIPs, and everything else is chat around the stream (Communities, Roles & Permissions).
Channel overwrite: per-channel allow and deny bits for a role or a member, applied in a fixed order: the default role's (deny, then allow), the member's roles combined (all denies, then all allows), then the member's own (deny, then allow) (Communities, Roles & Permissions).
Chat search: search over messages sharded by who searches: server messages indexed by server, DMs by user with each DM stored once per participant, results filtered by the searcher's current channel permissions (Real-Time Chat).
Chronological graph feed: a feed of what the people and places a user chose posted, newest first, such as Bluesky's Following or a Discord channel (Feeds & Recommendations).
Closure table: thread storage in a side table holding every ancestor-descendant pair, good for arbitrary subtree queries at the cost of a row per ancestor on every write (Posts, Comments & Voting).
Code of conduct (moderators): rules the platform sets for volunteer moderators and enforces against them; Reddit's Moderator Code of Conduct actions include removing moderators, restricting a community and limiting posting, with 878 reports actioned in the second half of 2025 (Volunteer Moderation & Community Governance).
Cold start: serving users, items or communities with no history: interests asked at sign-up and popular-in-region candidates for new users, reserved exploration and a proving ground for new items, directories and onboarding picks for new communities (Feeds & Recommendations).
Community ban: a penalty scoped to one community with community_id set, appealed to the community's moderators through modmail first, not an account penalty (Volunteer Moderation & Community Governance).
Community rules: rules a community adds on top of sitewide rules, published as versioned text and cited in removal notices; they can be stricter than sitewide policy, never looser (Volunteer Moderation & Community Governance).
Community-level enforcement: the platform quarantining, restricting or banning a whole community that won't enforce sitewide rules; Reddit banned 605,570 communities in the second half of 2025, 76.7% of them for spam (Volunteer Moderation & Community Governance).
Community-ranked feed: a feed ranked by a community's votes, such as a Reddit community's hot list (Feeds & Recommendations).
Confidence: Reddit's "best" sort: the lower bound of the Wilson score interval for the share of upvotes, which rewards comments whose quality is likely given how few votes they have, and ignores age (Posts, Comments & Voting).
Content rating: the platform's gating summary of an item or community (general, mature, adult); a community's rating is a floor, and an item can be rated higher than its community but never lower (Posts, Comments & Voting).
Controversy: a sort that finds items that split the voters, scoring 500 up and 500 down at 1,000 and 1,000 up and 10 down at about 1.07; a reader's option, rarely a default (Posts, Comments & Voting).
Crosspost: a post that republishes another item into a new place; like every repost it holds a reference to the original, never a copy (Posts, Comments & Voting).
DAVE: Discord's protocol, announced September 17, 2024, that end-to-end encrypts audio and video in DMs, group DMs, voice channels and Go Live streams using a Messaging Layer Security group and per-sender media keys, while text stays under content moderation (Real-Time Chat).
Defederation: suspending a whole domain on the fediverse, so nothing from it is stored except usernames and existing follows are removed (Federation & Open Protocols).
Delete activity: the ActivityPub message a home server sends to every server that may hold a copy of a deleted post; receivers should remove it and may answer later requests with a Tombstone and 410 Gone, so erasure beyond your own servers is best effort (Federation & Open Protocols).
Deleted: the content state for an author's own removal of their item, shown to readers as a placeholder saying the author deleted it (Posts, Comments & Voting).
Deletion latency: the time from a removal decision to the item disappearing from search and cached answers, a safety property because a removed post that stays searchable is still published (Search & Discovery).
Devvit: Reddit's developer platform for apps that run on Reddit; when it announced the end of public API access, it offered an App Migration Program with a $1 million fund, $1,000 payments to apps that move and free hosting (Developer Platforms, APIs & Data Access).
DM settings per community: letting members refuse DMs from people whose only connection is a given community, closing the path from a large public server to a private conversation (Real-Time Chat).
Domain block: a fediverse admin's action on a whole server: reject media (no files processed), limit (all its accounts limited, follows become requests) or suspend (defederation) (Federation & Open Protocols).
Edit: a new content_revisions row that moves the item's pointer, while reports and decisions keep pointing at the revision they judged so an author can't edit a reported post into innocence (Posts, Comments & Voting).
Embedding: a vector a model makes from an image region or whole image so that visual similarity becomes distance; embeddings are per model version, so a new model means re-embedding the corpus (Search & Discovery).
Fan-out on read: building a following feed at read time by gathering recent posts from everyone the viewer follows, which makes writes cheap and reads expensive (Feeds & Recommendations).
Fan-out on write: pushing each new post's id into every follower's precomputed feed list when it's published, which makes reads cheap and writes expensive in proportion to follower count; platforms skip it for high-follower authors (Feeds & Recommendations).
Fediverse Enhancement Proposal (FEP): how ActivityPub implementations agree on features the specification leaves out, such as quote posts (Federation & Open Protocols).
Feed definition: a feed (the platform's own or a third-party generator) stored as data, including whether it's profiled, so the non-profiled option is a row every surface can be pointed at (Feeds & Recommendations).
Feed generator: an independent AT Protocol service that returns a ranked list of post identifiers for the AppView to hydrate, published as a record so anyone can build a feed and users subscribe to it like an account (Federation & Open Protocols).
Firehose: the combined stream of updates a relay collects from many PDSes on the AT Protocol, which AppViews index (Federation & Open Protocols).
Follow: a one-way edge needing no consent (to a person, community, tag or board), the primary input to following feeds and a strong recommendation signal (Feeds & Recommendations).
Followers collection: an ActivityPub actor's followers, the default audience its activities are delivered to (Federation & Open Protocols).
Forum: a community of posts, where membership is often a subscription more than a gate and content is meant to be found through indexing, ranking and recommendation (Communities, Roles & Permissions).
Freeze: a Mastodon action that stops a local account from being used while keeping its content (Federation & Open Protocols).
Freshness by intent: choosing a search result's time decay from the query's intent: hours-old posts for a news event, the best thread regardless of age for a how-to question (Search & Discovery).
Friend-request warning: an alert on friend requests from unfamiliar senders; Discord's UK changes show one when there are no mutual friends or only a shared server of under 200 members (Real-Time Chat).
Friendship: a mutual edge that one side requests and the other accepts, mattering more for who may message whom than for feeds (Feeds & Recommendations).
Gateway: the one connection a chat client opens to receive everything for every place it belongs (messages, typing, presence, member changes, voice state, moderation actions), with heartbeats, intents and resume (Real-Time Chat).
Group: a community shape between forums and servers, such as Facebook Groups: a feed of posts inside a membership gate, with admins, moderators and join questions (Communities, Roles & Permissions).
Heavy ranking: the recommendation stage in which a large model scores each remaining candidate with many features for several predicted outcomes, such as click, long view, like, save, reply, share, hide and report (Feeds & Recommendations).
Hidden: a temporary content state: collapsed by a spam filter, blurred behind a label, or held while a report is reviewed (Posts, Comments & Voting).
Hot: Reddit's published sort ranking by the logarithm of net score plus age in units of 45,000 seconds (12.5 hours), so a post needs ten times the score to hold its rank against one 12.5 hours newer (Posts, Comments & Voting).
HTTP Signatures: the de facto authentication of ActivityPub server-to-server requests: the sender signs with the actor's key and the receiver fetches the key from the actor document; Mastodon supports RFC 9421 HTTP Message Signatures by default since version 4.5.0 (Federation & Open Protocols).
Impression log: the record of every served feed page with each item's candidate source, model version, position and demotions, which the next model trains on and which answers what was recommended to whom (Feeds & Recommendations).
Inbox: the endpoint where an ActivityPub actor receives activities delivered by other servers (Federation & Open Protocols).
Index from events: feeding the search index from content and visibility life-cycle events rather than polling, with removals on a separate higher-priority path with its own latency target (Search & Discovery).
Installation: an app's presence in one community, granted permission bits that the installer must hold themselves and that moderators can narrow or end, stored as a range (Developer Platforms, APIs & Data Access).
Instance: a community that is also a host, such as a Mastodon server, where the community and the operator are the same party with the duties of both (Communities, Roles & Permissions).
Intents: the event groups a gateway client or bot declares it wants, as a bitfield, which cut fan-out at the source (Real-Time Chat).
Interactions: slash commands and context menus that deliver exactly the input a user chose to send an app, so most apps never need to read every message (Developer Platforms, APIs & Data Access).
Invite link: a link that lets a specific person or anyone holding it join, with an expiry and a maximum use count; recording which link each member used lets a leaked one be revoked and its users found (Communities, Roles & Permissions).
Join gate: a condition checked at the moment of joining a community (a verified email or phone, a minimum account age, rules accepted, a paid tier or an age check), stored as data with its version (Communities, Roles & Permissions).
Join policy: how people get into a community: open, by request with moderator approval, by invite, or gated on a condition (Communities, Roles & Permissions).
Karma: an account's accumulated score from votes, used as a gate for posting and sometimes as a payout input; it should be derived from votes that survived manipulation checks, exclude self-votes, and never be the only gate (Posts, Comments & Voting).
Label: a statement of what content contains so it can be blurred, hidden, kept from minors or kept from ads, kept as a row with its source: the author, moderators, the platform or a third-party labeler (Posts, Comments & Voting).
Labeler: an independent AT Protocol service that attaches signed labels to accounts and records, which users subscribe to as they would follow an account (Federation & Open Protocols).
Lexicon: a shared AT Protocol schema (com.atproto.* for repository sync, app.bsky.* for the social app) that lets independent services agree on record and API shapes (Federation & Open Protocols).
Light ranking: the recommendation stage in which a cheaper model trims thousands of candidates to hundreds before heavy ranking (Feeds & Recommendations).
Limit: a Mastodon action that shows an account only to its followers on that server; as a domain block, it limits every account from a server and turns follows into requests (Federation & Open Protocols).
Locked thread: a thread a moderator has closed to new replies, a control layered on top of content states (Posts, Comments & Voting).
Logged-out reader: a visitor who never signs in, usually from search, served related items computed per page and cached, with personalization only under consent; Reddit monetizes them with ads on conversation pages and in feeds (Feeds & Recommendations).
Mastodon account actions: a server's local actions on an account: mark media sensitive, freeze, limit or suspend (data kept 30 days before deletion), emailed to the user with one appeal within 20 days (Federation & Open Protocols).
Materialized path: thread storage in which each row stores its ancestry as a string or ltree, so a subtree is one ordered index range scan (Posts, Comments & Voting).
Member list (visible range): sending a client only the slice of a large community's member list on screen rather than presence for every member (Real-Time Chat).
Mesh: a real-time topology in which every participant sends to every other, which works for three or four people and not beyond (Voice & Live Rooms).
Message content intent: Discord's privileged intent that delivers message text to an app; without it, content fields arrive empty except in messages the app sent, DMs with it, messages that mention it and messages a context-menu command was used on (Developer Platforms, APIs & Data Access).
Message request: a separate inbox for DMs from strangers, opened only when the recipient accepts; Discord routes DMs from non-friends who share only servers of 200 or more members there, and ignoring a request never notifies the sender (Real-Time Chat).
Mixer (MCU): a real-time server that decodes every participant, mixes audio and tiles video, and sends each one combined stream: cheap for clients, expensive for the server, and slower (Voice & Live Rooms).
Mod log: the append-only record of every moderator action in a community, automated or manual, with the actor's rank and the rule and reason cited; the community's accountability record (Volunteer Moderation & Community Governance).
Mod queue: the queue of reported and automod-filtered items for a community's moderators, the playbook's reports and queues with a community scope (Volunteer Moderation & Community Governance).
Moderation recording: recording a room for safety review, kept briefly and listened to only on a report, with notice, short default retention and access logging; impossible server-side under end-to-end encryption (Voice & Live Rooms).
Moderator concentration cap: a limit on how many large communities one person may moderate, held as configuration by community size band; Reddit introduced one in 2025 (Volunteer Moderation & Community Governance).
Modmail: the conversation channel between members and a community's moderation team as a team, used for appeals, removal questions and reports, so a moderator's departure doesn't lose the conversation (Volunteer Moderation & Community Governance).
Mute: a one-way filter that hides the target from the muter's own feeds without telling anyone (Feeds & Recommendations).
Nested sets: thread storage with left and right numbers per node: fast reads, expensive inserts, and a poor fit for live threads (Posts, Comments & Voting).
Non-profiled feed: a feed option not based on profiling, which DSA Article 38 requires very large platforms to offer for each recommender system; built as a first-class mode stored on the account and honored on every surface (Feeds & Recommendations).
Notification budget: limits on recommendation-driven pushes: a per-user cap within a hard ceiling, quiet hours in the user's time zone, consent, and a re-check of eligibility at send time (Feeds & Recommendations).
On-platform app runtime: hosting developers' code inside the platform rather than serving an external API, so data never leaves, at the cost of sandboxing, quotas, review and availability becoming the platform's job (Developer Platforms, APIs & Data Access).
One-party consent: the US federal rule (18 U.S.C. 2511(2)(d)) that a party to a communication may record it; some states require all parties, so a room with participants from many states follows the strictest rule (Voice & Live Rooms).
Outbox: the collection an ActivityPub actor adds activities to when it posts, likes, follows or deletes (Federation & Open Protocols).
Ownership transfer: handing a community to a new owner, irreversible and treated like a payout account change: re-authentication, the recipient's confirmation, notice to moderators and a short window for the old owner to cancel (Communities, Roles & Permissions).
PDS (Personal Data Server): the AT Protocol service that hosts a user's repository of signed records and manages their identity (Federation & Open Protocols).
Pending review: the content state where a filter puts an item it isn't sure about (an automod rule, a new account's first post, a classifier's uncertain middle) until moderators approve or remove it (Posts, Comments & Voting).
Permission algorithm: the deterministic evaluation of a member's permissions in a channel: the owner has everything; base permissions from roles; channel overwrites in fixed order; implicit rules; and timeouts leaving only reading (Communities, Roles & Permissions).
Permission bits: permissions stored as bit flags; Discord defines flags from bit 0 to bit 52 and serializes the set as a string, so a signed 64-bit column will eventually run out (Communities, Roles & Permissions).
Personalized recommendation feed: a feed ranked by a model of each viewer, from candidates far beyond their graph, such as Pinterest Home Feed, X's For You and YouTube Home (Feeds & Recommendations).
PinSage: Pinterest's 2018 graph convolutional network over its pin-and-board graph that learns an embedding per pin, turning related-item retrieval into nearest-neighbor search (Feeds & Recommendations).
Pixie: Pinterest's 2017 system of in-memory random walks over the pin-and-board graph, generating candidates without a trained model (Feeds & Recommendations).
Platform staff access: a separate, audited, just-in-time grant that lets trust and safety, support and engineering staff act in any community without ever appearing as a role inside one (Communities, Roles & Permissions).
Policy demotion: a ranking penalty applied after scoring to allowed but borderline items, recorded as its own reason so it's explainable, countable and testable (Feeds & Recommendations).
Poll: a post format with options and a closing time, allowing one poll vote per account, kept apart from the item's up and down votes (Posts, Comments & Voting).
Portability: moving an account between hosts: on the AT Protocol the DID is repointed and the account, posts and followers move together; on Mastodon only followers move, posts stay behind, and the old account becomes inaccessible (Federation & Open Protocols).
Privileged intents: gateway event groups that need declaration and, at scale, approval: server presences, server members and message content; Discord requires verification for apps in 100 or more servers and approval of each privileged intent (Developer Platforms, APIs & Data Access).
Proving ground: a "new" or "rising" pool seen by a small share of readers, from which posts that beat the section's baseline graduate to the main gallery; where vote-ring detection has to run first (Posts, Comments & Voting).
Query log: a user's search history, personal data kept raw only briefly, then aggregated or de-identified, with safety-list matches counted separately and the history included in export and erasure (Search & Discovery).
Rank: a role's position, deciding whom an actor can act on: assign only roles below their own highest, edit only lower roles, grant only permissions they hold, and kick, ban or rename only members below them; rank doesn't affect permission math (Communities, Roles & Permissions).
Re-engagement notification: a push or email that recommends content rather than reporting something addressed to the user, chosen by the same ranking models as the feed and needing its own budget (Feeds & Recommendations).
Read state: a member's last-read message per channel, updated on every scroll, batched per session and written behind, from which unread badges are derived (Real-Time Chat).
Reblog: a repost that adds the reposter's own commentary on top of the chain before it, the mechanism Tumblr built its distribution on (Posts, Comments & Voting).
Recording consent: notice before capture and a visible indicator throughout a recorded room, with a consent record per participant per session; a participant who declines listens without speaking, and apps that capture follow the same rule (Voice & Live Rooms).
Relay: an AT Protocol service that collects updates from many PDSes into one combined stream, the firehose (Federation & Open Protocols).
Remote actor: a user from another federated server, mirrored as a shadow accounts row with no login so posts, follows, reports and penalties reference one kind of account (Federation & Open Protocols).
Removal reason: a reason a community defines (usually one per rule) that a moderator picks when removing and the author's notice states (Volunteer Moderation & Community Governance).
Removed: the content state for a moderator's or the platform's removal; the author usually still sees the item and a notice of why, and everyone else sees a placeholder saying it was removed (Posts, Comments & Voting).
Repost: a post pointing at another item; the original controls the copy, so when it's removed or deleted every repost and quote stops showing its content (Posts, Comments & Voting).
Request coalescing: answering concurrent requests for the same rows with a single database query whose result they all share, Discord's defense against hot channels (Real-Time Chat).
Researcher access: the DSA duty (Article 40) for very large platforms to give vetted researchers data on systemic risks on a coordinator's reasoned request, and access without undue delay to publicly accessible data; the Commission adopted the delegated act on July 2, 2025 (Developer Platforms, APIs & Data Access).
Resume: reconnecting a dropped gateway session with its session id and last sequence number so the server replays what was missed instead of a full reload (Real-Time Chat).
Retraction by negation: withdrawing an AT Protocol label by publishing the same source, subject and value with neg set, which keeps the history auditable (Federation & Open Protocols).
Selective forwarding unit (SFU): a real-time server that receives each participant's stream and forwards the ones each receiver needs without decoding them, paired with simulcast or scalable video coding; community platforms use SFUs (Voice & Live Rooms).
Self-label: a label the author sets on their own content; on the AT Protocol its authenticity comes from the repository's signature (Posts, Comments & Voting).
Sensitive-media blur: blurring unsolicited images by default for teens and as a setting for adults; Discord's Teen Safety Assist turned it on in October 2023 (Real-Time Chat).
Server: a community of channels, where membership is a gate and each channel decides who among the members can see it; most content isn't meant to be found by outsiders (Communities, Roles & Permissions).
Server Subscriptions: Discord's paid community tiers giving members subscriber-only channels and roles, granted and revoked by the subscription's events, with eligibility rules for the owner (Communities, Roles & Permissions).
Shared inbox: a server-wide ActivityPub inbox to which a sender delivers one copy per server for public and follower-addressed activities instead of one per follower (Federation & Open Protocols).
Simulcast: a sender uploading several qualities of the same stream so an SFU can forward each receiver the one it can handle; scalable video coding does the same with one layered stream (Voice & Live Rooms).
Slowmode: a per-channel minimum interval between a member's messages, from 0 to 21,600 seconds on Discord and also limiting thread creation, with a bypass permission for moderators (Real-Time Chat).
Snowflake: Discord's 64-bit id whose top 42 bits are milliseconds since the platform's epoch, followed by worker, process and sequence bits, so ids sort by time and need no coordination to generate (Real-Time Chat).
Sockpuppet: an alternate account used to vote for oneself (Posts, Comments & Voting).
Stackable moderation: Bluesky's model in which users subscribe to moderation services, its own by default as a floor, and add independent labelers whose labels they configure to hide, blur or warn (Federation & Open Protocols).
Stage: a room that separates a few speakers from an audience, with moderators inviting and removing speakers and listeners requesting to speak; Discord's stages allow up to 10,000 listeners (Voice & Live Rooms).
Suspend: a Mastodon action removing an account from public view with its data kept 30 days before permanent deletion; as a domain block, it defederates a server (Federation & Open Protocols).
Tags and hashtags: user-supplied facets normalized like handles, capped per item and moderated as content, because a tag can become a meeting point for prohibited content (Search & Discovery).
Three searches: community search as three problems: content (posts and comments), places (communities and channels) and people (accounts and handles), each with its own ranking and safety rules (Search & Discovery).
Timeout: a community penalty that strips every permission except viewing the channel and reading history, with owners and administrators exempt; stored as a feature restriction, so it expires with no clean-up (Communities, Roles & Permissions).
Tombstone (comment): the placeholder a removed or deleted comment leaves in its thread, keeping its place so replies still have a parent, while its text is cleared from what's served (Posts, Comments & Voting).
TransAct: Pinterest's 2023 transformer over a user's real-time sequence of recent actions, combined with batch-computed long-term embeddings, used in Homefeed, Related Pins, Notifications and Search (Feeds & Recommendations).
Translation (machine): a derived rendering of a post in another language, labeled as machine-translated, invalidated when the original changes, kept out of evidence, and recorded with the engine and version that produced it (Search & Discovery).
Two tiers of rules: sitewide rules that apply everywhere plus community rules on top; every removal records which tier and rule it enforced, and a community can be stricter but never looser (Volunteer Moderation & Community Governance).
Typeahead: prefix search on community names and normalized handles, ranked by size and activity, filtered for visibility and blocks, and conservative about minors (Search & Discovery).
Value model: the weights that combine a heavy ranker's predicted outcomes into one score, including negative weights on hides, reports and unfollows; the platform's editorial policy expressed as arithmetic (Feeds & Recommendations).
Visual search: answering "more like this" and "what is this" for images through object detection, embeddings, approximate nearest-neighbor search and re-ranking with safety filters (Search & Discovery).
Voice channel: a persistent room inside a community that members drop in and out of without a host; Discord's allow up to 99 users (Voice & Live Rooms).
Vote: one account's judgment of one item (up, down or withdrawn), stored as a row so a later finding can discount it and recompute scores and karma; on Reddit every item starts with its author's upvote (Posts, Comments & Voting).
Vote discount: zeroing a set of votes found to be manipulated and recomputing scores and karma, possible because votes are rows and scores are derived (Posts, Comments & Voting).
Votes per view: votes divided by discounted views, a better quality signal for gallery ranking than raw votes (Posts, Comments & Voting).
Workplace chat: chat such as Slack or Microsoft Teams that runs the community architecture with the duties inverted: the customer organization controls the data, moderates, sets retention and legal holds and answers legal requests (Real-Time Chat).

2023 blackout: the June 12, 2023 protest in which thousands of Reddit communities (over 7,800 by one count) went private or restricted posting over Data API pricing, showing that moderators control availability and their tools are infrastructure (Volunteer Moderation & Community Governance).
Abandonment: a community whose owner and moderators have stopped moderating and is drifting into spam; the platform hands it to an active member (checked against the owner's recent activity, with notice to the owner) or closes it (Communities, Roles & Permissions).
ActivityPub: the W3C Recommendation (since January 23, 2018) behind Mastodon, the wider fediverse and Threads' opt-in federation, in which servers deliver activities such as Create, Follow and Delete to each other's inboxes by HTTP POST (Federation & Open Protocols).
Actor: in ActivityPub, a user, group or service with an inbox and an outbox; posting adds an activity to the outbox and federation delivers it to recipients' inboxes (Federation & Open Protocols).
Adjacency list: thread storage where each comment points at its parent and a subtree is read with a recursive query; paired with a materialized path, it's the default here (Posts, Comments & Voting).
ADMINISTRATOR: the Discord permission bit that grants every permission and skips channel overwrites entirely (Communities, Roles & Permissions).
AI answer: an answer a model composes from retrieved community threads, shown only with citations to the items it drew on and held to search's filters, so a removal of any cited item invalidates every cached answer citing it (Search & Discovery).
Answer-ness: a search ranking signal that favors, for question-shaped queries, threads with accepted or highly voted answers over threads with only the question (Search & Discovery).
API pricing: charging developers for API access; Reddit's terms effective July 1, 2023 kept free limits per OAuth client and charged $0.24 per 1,000 calls above them, with moderation tools exempted (Developer Platforms, APIs & Data Access).
AppView: an AT Protocol service that indexes the network from the firehose and serves the aggregated views apps need: threads, like and repost counts, follower lists, search (Federation & Open Protocols).
Archiving: closing old threads to new comments and votes after a period, which caps the surface spammers and manipulators can reach and lets scores freeze (Posts, Comments & Voting).
AT Protocol: Bluesky's protocol, which separates where a user's data lives (a PDS) from the relays, AppViews, feed generators and labelers that index, rank and moderate it (Federation & Open Protocols).
Automation share: the share of moderator actions made by automated tools; 68.6% of Reddit moderators' removals in the second half of 2025 were automated (Volunteer Moderation & Community Governance).
Automod: a rules engine that volunteer moderators configure to remove, hold or report posts and comments matching conditions on the item and its author's account; it should offer structured rules first, linear-time regular expressions second, hard limits, a report-only mode and attribution of every action to its rule (Volunteer Moderation & Community Governance).
AutoMod (Discord): Discord's structured automod with published limits per server: six keyword rules (up to 1,000 keywords and 10 regular expressions each) and one each for spam, keyword presets, mention spam and member profiles, with block, alert, timeout and block-interactions actions (Volunteer Moderation & Community Governance).
AutoModerator: Reddit's per-community rules engine, configured by moderators, that removes, holds or reports items matching conditions on the item and on its author's account, such as account age and reputation (Volunteer Moderation & Community Governance).
Base permissions: the first step of the permission algorithm: the default role's permissions ORed with those of every role the member holds (Communities, Roles & Permissions).
Block: a one-way filter that hides each account from the other everywhere (feeds, replies, search, mentions, recommendations, chat), enforced in every service in both directions (Feeds & Recommendations).
Blocklist (federation): a list of domain blocks shared between fediverse admins as a CSV file; it cuts off bad servers fast but propagates errors as fast, so imports should record their source and be reviewed (Federation & Open Protocols).
Bot sharding: splitting a bot's gateway connections across shards, which Discord requires from 2,500 servers, assigning each server by shard_id = (guild_id >> 22) % num_shards (Real-Time Chat).
Bridgy Fed: a bridge between ActivityPub, the AT Protocol and the web, opt-in per user: bridging is off until the user enables it and off again when they block it (Federation & Open Protocols).
Brigading: members of one community descending on another to vote or comment, answered with links that don't allow voting from the referral and tools that show moderators where a surge came from (Posts, Comments & Voting).
Bucket: a time window (about ten days in Discord's design) that, combined with the channel id, forms a message partition key so no partition grows past a comfortable size (Real-Time Chat).
Candidate generation: the first recommendation stage, in which several sources (the viewer's graph, similar users, embedding neighbors, related and trending items) each cheaply propose hundreds to thousands of items (Feeds & Recommendations).
Category: a channel that holds other channels and carries permission overwrites they can inherit (Communities, Roles & Permissions).
Category sync: a channel following its category's overwrites, so changing the category changes every synced channel; editing the child's own overwrites breaks the sync (Communities, Roles & Permissions).
Channel: a conversation space inside a community with its own audience, kind (text, forum, announcement, voice, stage, category) and permission overwrites (Communities, Roles & Permissions).
Channel (streaming): one person's community on a streaming platform: the broadcaster owns it, appoints moderators and VIPs, and everything else is chat around the stream (Communities, Roles & Permissions).
Channel overwrite: per-channel allow and deny bits for a role or a member, applied in a fixed order: the default role's (deny, then allow), the member's roles combined (all denies, then all allows), then the member's own (deny, then allow) (Communities, Roles & Permissions).
Chat search: search over messages sharded by who searches: server messages indexed by server, DMs by user with each DM stored once per participant, results filtered by the searcher's current channel permissions (Real-Time Chat).
Chronological graph feed: a feed of what the people and places a user chose posted, newest first, such as Bluesky's Following or a Discord channel (Feeds & Recommendations).
Closure table: thread storage in a side table holding every ancestor-descendant pair, good for arbitrary subtree queries at the cost of a row per ancestor on every write (Posts, Comments & Voting).
Code of conduct (moderators): rules the platform sets for volunteer moderators and enforces against them; Reddit's Moderator Code of Conduct actions include removing moderators, restricting a community and limiting posting, with 878 reports actioned in the second half of 2025 (Volunteer Moderation & Community Governance).
Cold start: serving users, items or communities with no history: interests asked at sign-up and popular-in-region candidates for new users, reserved exploration and a proving ground for new items, directories and onboarding picks for new communities (Feeds & Recommendations).
Community ban: a penalty scoped to one community with community_id set, appealed to the community's moderators through modmail first, not an account penalty (Volunteer Moderation & Community Governance).
Community rules: rules a community adds on top of sitewide rules, published as versioned text and cited in removal notices; they can be stricter than sitewide policy, never looser (Volunteer Moderation & Community Governance).
Community-level enforcement: the platform quarantining, restricting or banning a whole community that won't enforce sitewide rules; Reddit banned 605,570 communities in the second half of 2025, 76.7% of them for spam (Volunteer Moderation & Community Governance).
Community-ranked feed: a feed ranked by a community's votes, such as a Reddit community's hot list (Feeds & Recommendations).
Confidence: Reddit's "best" sort: the lower bound of the Wilson score interval for the share of upvotes, which rewards comments whose quality is likely given how few votes they have, and ignores age (Posts, Comments & Voting).
Content rating: the platform's gating summary of an item or community (general, mature, adult); a community's rating is a floor, and an item can be rated higher than its community but never lower (Posts, Comments & Voting).
Controversy: a sort that finds items that split the voters, scoring 500 up and 500 down at 1,000 and 1,000 up and 10 down at about 1.07; a reader's option, rarely a default (Posts, Comments & Voting).
Crosspost: a post that republishes another item into a new place; like every repost it holds a reference to the original, never a copy (Posts, Comments & Voting).
DAVE: Discord's protocol, announced September 17, 2024, that end-to-end encrypts audio and video in DMs, group DMs, voice channels and Go Live streams using a Messaging Layer Security group and per-sender media keys, while text stays under content moderation (Real-Time Chat).
Defederation: suspending a whole domain on the fediverse, so nothing from it is stored except usernames and existing follows are removed (Federation & Open Protocols).
Delete activity: the ActivityPub message a home server sends to every server that may hold a copy of a deleted post; receivers should remove it and may answer later requests with a Tombstone and 410 Gone, so erasure beyond your own servers is best effort (Federation & Open Protocols).
Deleted: the content state for an author's own removal of their item, shown to readers as a placeholder saying the author deleted it (Posts, Comments & Voting).
Deletion latency: the time from a removal decision to the item disappearing from search and cached answers, a safety property because a removed post that stays searchable is still published (Search & Discovery).
Devvit: Reddit's developer platform for apps that run on Reddit; when it announced the end of public API access, it offered an App Migration Program with a $1 million fund, $1,000 payments to apps that move and free hosting (Developer Platforms, APIs & Data Access).
DM settings per community: letting members refuse DMs from people whose only connection is a given community, closing the path from a large public server to a private conversation (Real-Time Chat).
Domain block: a fediverse admin's action on a whole server: reject media (no files processed), limit (all its accounts limited, follows become requests) or suspend (defederation) (Federation & Open Protocols).
Edit: a new content_revisions row that moves the item's pointer, while reports and decisions keep pointing at the revision they judged so an author can't edit a reported post into innocence (Posts, Comments & Voting).
Embedding: a vector a model makes from an image region or whole image so that visual similarity becomes distance; embeddings are per model version, so a new model means re-embedding the corpus (Search & Discovery).
Fan-out on read: building a following feed at read time by gathering recent posts from everyone the viewer follows, which makes writes cheap and reads expensive (Feeds & Recommendations).
Fan-out on write: pushing each new post's id into every follower's precomputed feed list when it's published, which makes reads cheap and writes expensive in proportion to follower count; platforms skip it for high-follower authors (Feeds & Recommendations).
Fediverse Enhancement Proposal (FEP): how ActivityPub implementations agree on features the specification leaves out, such as quote posts (Federation & Open Protocols).
Feed definition: a feed (the platform's own or a third-party generator) stored as data, including whether it's profiled, so the non-profiled option is a row every surface can be pointed at (Feeds & Recommendations).
Feed generator: an independent AT Protocol service that returns a ranked list of post identifiers for the AppView to hydrate, published as a record so anyone can build a feed and users subscribe to it like an account (Federation & Open Protocols).
Firehose: the combined stream of updates a relay collects from many PDSes on the AT Protocol, which AppViews index (Federation & Open Protocols).
Follow: a one-way edge needing no consent (to a person, community, tag or board), the primary input to following feeds and a strong recommendation signal (Feeds & Recommendations).
Followers collection: an ActivityPub actor's followers, the default audience its activities are delivered to (Federation & Open Protocols).
Forum: a community of posts, where membership is often a subscription more than a gate and content is meant to be found through indexing, ranking and recommendation (Communities, Roles & Permissions).
Freeze: a Mastodon action that stops a local account from being used while keeping its content (Federation & Open Protocols).
Freshness by intent: choosing a search result's time decay from the query's intent: hours-old posts for a news event, the best thread regardless of age for a how-to question (Search & Discovery).
Friend-request warning: an alert on friend requests from unfamiliar senders; Discord's UK changes show one when there are no mutual friends or only a shared server of under 200 members (Real-Time Chat).
Friendship: a mutual edge that one side requests and the other accepts, mattering more for who may message whom than for feeds (Feeds & Recommendations).
Gateway: the one connection a chat client opens to receive everything for every place it belongs (messages, typing, presence, member changes, voice state, moderation actions), with heartbeats, intents and resume (Real-Time Chat).
Group: a community shape between forums and servers, such as Facebook Groups: a feed of posts inside a membership gate, with admins, moderators and join questions (Communities, Roles & Permissions).
Heavy ranking: the recommendation stage in which a large model scores each remaining candidate with many features for several predicted outcomes, such as click, long view, like, save, reply, share, hide and report (Feeds & Recommendations).
Hidden: a temporary content state: collapsed by a spam filter, blurred behind a label, or held while a report is reviewed (Posts, Comments & Voting).
Hot: Reddit's published sort ranking by the logarithm of net score plus age in units of 45,000 seconds (12.5 hours), so a post needs ten times the score to hold its rank against one 12.5 hours newer (Posts, Comments & Voting).
HTTP Signatures: the de facto authentication of ActivityPub server-to-server requests: the sender signs with the actor's key and the receiver fetches the key from the actor document; Mastodon supports RFC 9421 HTTP Message Signatures by default since version 4.5.0 (Federation & Open Protocols).
Impression log: the record of every served feed page with each item's candidate source, model version, position and demotions, which the next model trains on and which answers what was recommended to whom (Feeds & Recommendations).
Inbox: the endpoint where an ActivityPub actor receives activities delivered by other servers (Federation & Open Protocols).
Index from events: feeding the search index from content and visibility life-cycle events rather than polling, with removals on a separate higher-priority path with its own latency target (Search & Discovery).
Installation: an app's presence in one community, granted permission bits that the installer must hold themselves and that moderators can narrow or end, stored as a range (Developer Platforms, APIs & Data Access).
Instance: a community that is also a host, such as a Mastodon server, where the community and the operator are the same party with the duties of both (Communities, Roles & Permissions).
Intents: the event groups a gateway client or bot declares it wants, as a bitfield, which cut fan-out at the source (Real-Time Chat).
Interactions: slash commands and context menus that deliver exactly the input a user chose to send an app, so most apps never need to read every message (Developer Platforms, APIs & Data Access).
Invite link: a link that lets a specific person or anyone holding it join, with an expiry and a maximum use count; recording which link each member used lets a leaked one be revoked and its users found (Communities, Roles & Permissions).
Join gate: a condition checked at the moment of joining a community (a verified email or phone, a minimum account age, rules accepted, a paid tier or an age check), stored as data with its version (Communities, Roles & Permissions).
Join policy: how people get into a community: open, by request with moderator approval, by invite, or gated on a condition (Communities, Roles & Permissions).
Karma: an account's accumulated score from votes, used as a gate for posting and sometimes as a payout input; it should be derived from votes that survived manipulation checks, exclude self-votes, and never be the only gate (Posts, Comments & Voting).
Label: a statement of what content contains so it can be blurred, hidden, kept from minors or kept from ads, kept as a row with its source: the author, moderators, the platform or a third-party labeler (Posts, Comments & Voting).
Labeler: an independent AT Protocol service that attaches signed labels to accounts and records, which users subscribe to as they would follow an account (Federation & Open Protocols).
Lexicon: a shared AT Protocol schema (com.atproto.* for repository sync, app.bsky.* for the social app) that lets independent services agree on record and API shapes (Federation & Open Protocols).
Light ranking: the recommendation stage in which a cheaper model trims thousands of candidates to hundreds before heavy ranking (Feeds & Recommendations).
Limit: a Mastodon action that shows an account only to its followers on that server; as a domain block, it limits every account from a server and turns follows into requests (Federation & Open Protocols).
Locked thread: a thread a moderator has closed to new replies, a control layered on top of content states (Posts, Comments & Voting).
Logged-out reader: a visitor who never signs in, usually from search, served related items computed per page and cached, with personalization only under consent; Reddit monetizes them with ads on conversation pages and in feeds (Feeds & Recommendations).
Mastodon account actions: a server's local actions on an account: mark media sensitive, freeze, limit or suspend (data kept 30 days before deletion), emailed to the user with one appeal within 20 days (Federation & Open Protocols).
Materialized path: thread storage in which each row stores its ancestry as a string or ltree, so a subtree is one ordered index range scan (Posts, Comments & Voting).
Member list (visible range): sending a client only the slice of a large community's member list on screen rather than presence for every member (Real-Time Chat).
Mesh: a real-time topology in which every participant sends to every other, which works for three or four people and not beyond (Voice & Live Rooms).
Message content intent: Discord's privileged intent that delivers message text to an app; without it, content fields arrive empty except in messages the app sent, DMs with it, messages that mention it and messages a context-menu command was used on (Developer Platforms, APIs & Data Access).
Message request: a separate inbox for DMs from strangers, opened only when the recipient accepts; Discord routes DMs from non-friends who share only servers of 200 or more members there, and ignoring a request never notifies the sender (Real-Time Chat).
Mixer (MCU): a real-time server that decodes every participant, mixes audio and tiles video, and sends each one combined stream: cheap for clients, expensive for the server, and slower (Voice & Live Rooms).
Mod log: the append-only record of every moderator action in a community, automated or manual, with the actor's rank and the rule and reason cited; the community's accountability record (Volunteer Moderation & Community Governance).
Mod queue: the queue of reported and automod-filtered items for a community's moderators, the playbook's reports and queues with a community scope (Volunteer Moderation & Community Governance).
Moderation recording: recording a room for safety review, kept briefly and listened to only on a report, with notice, short default retention and access logging; impossible server-side under end-to-end encryption (Voice & Live Rooms).
Moderator concentration cap: a limit on how many large communities one person may moderate, held as configuration by community size band; Reddit introduced one in 2025 (Volunteer Moderation & Community Governance).
Modmail: the conversation channel between members and a community's moderation team as a team, used for appeals, removal questions and reports, so a moderator's departure doesn't lose the conversation (Volunteer Moderation & Community Governance).
Mute: a one-way filter that hides the target from the muter's own feeds without telling anyone (Feeds & Recommendations).
Nested sets: thread storage with left and right numbers per node: fast reads, expensive inserts, and a poor fit for live threads (Posts, Comments & Voting).
Non-profiled feed: a feed option not based on profiling, which DSA Article 38 requires very large platforms to offer for each recommender system; built as a first-class mode stored on the account and honored on every surface (Feeds & Recommendations).
Notification budget: limits on recommendation-driven pushes: a per-user cap within a hard ceiling, quiet hours in the user's time zone, consent, and a re-check of eligibility at send time (Feeds & Recommendations).
On-platform app runtime: hosting developers' code inside the platform rather than serving an external API, so data never leaves, at the cost of sandboxing, quotas, review and availability becoming the platform's job (Developer Platforms, APIs & Data Access).
One-party consent: the US federal rule (18 U.S.C. 2511(2)(d)) that a party to a communication may record it; some states require all parties, so a room with participants from many states follows the strictest rule (Voice & Live Rooms).
Outbox: the collection an ActivityPub actor adds activities to when it posts, likes, follows or deletes (Federation & Open Protocols).
Ownership transfer: handing a community to a new owner, irreversible and treated like a payout account change: re-authentication, the recipient's confirmation, notice to moderators and a short window for the old owner to cancel (Communities, Roles & Permissions).
PDS (Personal Data Server): the AT Protocol service that hosts a user's repository of signed records and manages their identity (Federation & Open Protocols).
Pending review: the content state where a filter puts an item it isn't sure about (an automod rule, a new account's first post, a classifier's uncertain middle) until moderators approve or remove it (Posts, Comments & Voting).
Permission algorithm: the deterministic evaluation of a member's permissions in a channel: the owner has everything; base permissions from roles; channel overwrites in fixed order; implicit rules; and timeouts leaving only reading (Communities, Roles & Permissions).
Permission bits: permissions stored as bit flags; Discord defines flags from bit 0 to bit 52 and serializes the set as a string, so a signed 64-bit column will eventually run out (Communities, Roles & Permissions).
Personalized recommendation feed: a feed ranked by a model of each viewer, from candidates far beyond their graph, such as Pinterest Home Feed, X's For You and YouTube Home (Feeds & Recommendations).
PinSage: Pinterest's 2018 graph convolutional network over its pin-and-board graph that learns an embedding per pin, turning related-item retrieval into nearest-neighbor search (Feeds & Recommendations).
Pixie: Pinterest's 2017 system of in-memory random walks over the pin-and-board graph, generating candidates without a trained model (Feeds & Recommendations).
Platform staff access: a separate, audited, just-in-time grant that lets trust and safety, support and engineering staff act in any community without ever appearing as a role inside one (Communities, Roles & Permissions).
Policy demotion: a ranking penalty applied after scoring to allowed but borderline items, recorded as its own reason so it's explainable, countable and testable (Feeds & Recommendations).
Poll: a post format with options and a closing time, allowing one poll vote per account, kept apart from the item's up and down votes (Posts, Comments & Voting).
Portability: moving an account between hosts: on the AT Protocol the DID is repointed and the account, posts and followers move together; on Mastodon only followers move, posts stay behind, and the old account becomes inaccessible (Federation & Open Protocols).
Privileged intents: gateway event groups that need declaration and, at scale, approval: server presences, server members and message content; Discord requires verification for apps in 100 or more servers and approval of each privileged intent (Developer Platforms, APIs & Data Access).
Proving ground: a "new" or "rising" pool seen by a small share of readers, from which posts that beat the section's baseline graduate to the main gallery; where vote-ring detection has to run first (Posts, Comments & Voting).
Query log: a user's search history, personal data kept raw only briefly, then aggregated or de-identified, with safety-list matches counted separately and the history included in export and erasure (Search & Discovery).
Rank: a role's position, deciding whom an actor can act on: assign only roles below their own highest, edit only lower roles, grant only permissions they hold, and kick, ban or rename only members below them; rank doesn't affect permission math (Communities, Roles & Permissions).
Re-engagement notification: a push or email that recommends content rather than reporting something addressed to the user, chosen by the same ranking models as the feed and needing its own budget (Feeds & Recommendations).
Read state: a member's last-read message per channel, updated on every scroll, batched per session and written behind, from which unread badges are derived (Real-Time Chat).
Reblog: a repost that adds the reposter's own commentary on top of the chain before it, the mechanism Tumblr built its distribution on (Posts, Comments & Voting).
Recording consent: notice before capture and a visible indicator throughout a recorded room, with a consent record per participant per session; a participant who declines listens without speaking, and apps that capture follow the same rule (Voice & Live Rooms).
Relay: an AT Protocol service that collects updates from many PDSes into one combined stream, the firehose (Federation & Open Protocols).
Remote actor: a user from another federated server, mirrored as a shadow accounts row with no login so posts, follows, reports and penalties reference one kind of account (Federation & Open Protocols).
Removal reason: a reason a community defines (usually one per rule) that a moderator picks when removing and the author's notice states (Volunteer Moderation & Community Governance).
Removed: the content state for a moderator's or the platform's removal; the author usually still sees the item and a notice of why, and everyone else sees a placeholder saying it was removed (Posts, Comments & Voting).
Repost: a post pointing at another item; the original controls the copy, so when it's removed or deleted every repost and quote stops showing its content (Posts, Comments & Voting).
Request coalescing: answering concurrent requests for the same rows with a single database query whose result they all share, Discord's defense against hot channels (Real-Time Chat).
Researcher access: the DSA duty (Article 40) for very large platforms to give vetted researchers data on systemic risks on a coordinator's reasoned request, and access without undue delay to publicly accessible data; the Commission adopted the delegated act on July 2, 2025 (Developer Platforms, APIs & Data Access).
Resume: reconnecting a dropped gateway session with its session id and last sequence number so the server replays what was missed instead of a full reload (Real-Time Chat).
Retraction by negation: withdrawing an AT Protocol label by publishing the same source, subject and value with neg set, which keeps the history auditable (Federation & Open Protocols).
Selective forwarding unit (SFU): a real-time server that receives each participant's stream and forwards the ones each receiver needs without decoding them, paired with simulcast or scalable video coding; community platforms use SFUs (Voice & Live Rooms).
Self-label: a label the author sets on their own content; on the AT Protocol its authenticity comes from the repository's signature (Posts, Comments & Voting).
Sensitive-media blur: blurring unsolicited images by default for teens and as a setting for adults; Discord's Teen Safety Assist turned it on in October 2023 (Real-Time Chat).
Server: a community of channels, where membership is a gate and each channel decides who among the members can see it; most content isn't meant to be found by outsiders (Communities, Roles & Permissions).
Server Subscriptions: Discord's paid community tiers giving members subscriber-only channels and roles, granted and revoked by the subscription's events, with eligibility rules for the owner (Communities, Roles & Permissions).
Shared inbox: a server-wide ActivityPub inbox to which a sender delivers one copy per server for public and follower-addressed activities instead of one per follower (Federation & Open Protocols).
Simulcast: a sender uploading several qualities of the same stream so an SFU can forward each receiver the one it can handle; scalable video coding does the same with one layered stream (Voice & Live Rooms).
Slowmode: a per-channel minimum interval between a member's messages, from 0 to 21,600 seconds on Discord and also limiting thread creation, with a bypass permission for moderators (Real-Time Chat).
Snowflake: Discord's 64-bit id whose top 42 bits are milliseconds since the platform's epoch, followed by worker, process and sequence bits, so ids sort by time and need no coordination to generate (Real-Time Chat).
Sockpuppet: an alternate account used to vote for oneself (Posts, Comments & Voting).
Stackable moderation: Bluesky's model in which users subscribe to moderation services, its own by default as a floor, and add independent labelers whose labels they configure to hide, blur or warn (Federation & Open Protocols).
Stage: a room that separates a few speakers from an audience, with moderators inviting and removing speakers and listeners requesting to speak; Discord's stages allow up to 10,000 listeners (Voice & Live Rooms).
Suspend: a Mastodon action removing an account from public view with its data kept 30 days before permanent deletion; as a domain block, it defederates a server (Federation & Open Protocols).
Tags and hashtags: user-supplied facets normalized like handles, capped per item and moderated as content, because a tag can become a meeting point for prohibited content (Search & Discovery).
Three searches: community search as three problems: content (posts and comments), places (communities and channels) and people (accounts and handles), each with its own ranking and safety rules (Search & Discovery).
Timeout: a community penalty that strips every permission except viewing the channel and reading history, with owners and administrators exempt; stored as a feature restriction, so it expires with no clean-up (Communities, Roles & Permissions).
Tombstone (comment): the placeholder a removed or deleted comment leaves in its thread, keeping its place so replies still have a parent, while its text is cleared from what's served (Posts, Comments & Voting).
TransAct: Pinterest's 2023 transformer over a user's real-time sequence of recent actions, combined with batch-computed long-term embeddings, used in Homefeed, Related Pins, Notifications and Search (Feeds & Recommendations).
Translation (machine): a derived rendering of a post in another language, labeled as machine-translated, invalidated when the original changes, kept out of evidence, and recorded with the engine and version that produced it (Search & Discovery).
Two tiers of rules: sitewide rules that apply everywhere plus community rules on top; every removal records which tier and rule it enforced, and a community can be stricter but never looser (Volunteer Moderation & Community Governance).
Typeahead: prefix search on community names and normalized handles, ranked by size and activity, filtered for visibility and blocks, and conservative about minors (Search & Discovery).
Value model: the weights that combine a heavy ranker's predicted outcomes into one score, including negative weights on hides, reports and unfollows; the platform's editorial policy expressed as arithmetic (Feeds & Recommendations).
Visual search: answering "more like this" and "what is this" for images through object detection, embeddings, approximate nearest-neighbor search and re-ranking with safety filters (Search & Discovery).
Voice channel: a persistent room inside a community that members drop in and out of without a host; Discord's allow up to 99 users (Voice & Live Rooms).
Vote: one account's judgment of one item (up, down or withdrawn), stored as a row so a later finding can discount it and recompute scores and karma; on Reddit every item starts with its author's upvote (Posts, Comments & Voting).
Vote discount: zeroing a set of votes found to be manipulated and recomputing scores and karma, possible because votes are rows and scores are derived (Posts, Comments & Voting).
Votes per view: votes divided by discounted views, a better quality signal for gallery ranking than raw votes (Posts, Comments & Voting).
Workplace chat: chat such as Slack or Microsoft Teams that runs the community architecture with the duties inverted: the customer organization controls the data, moderates, sets retention and legal holds and answers legal requests (Real-Time Chat).