Running the Platform Glossary · UGC Platforms

410 Gone: the status a removed item's URL answers when it was removed for policy, deleted by its author or purged, with a coarse public reason in the body (Migrations, Purges & Shutdowns).
Acceptance rate: the share of booking requests hosts accept, with median response time and the share that expire; a request-to-book marketplace with a low rate fails guests even when search converts (Operating Metrics).
Active supply: the creators, streamers, sellers, hosts or listings active in a period, the leading indicator for creator and marketplace businesses (Operating Metrics).
Activity fact: one row per identity (account or anonymous identifier) per day it was active, from which DAU, DAUq-style counts, MAU and the DSA's EU recipients are all different queries (Operating Metrics).
AI answers: a model answering questions over the platform's own corpus, such as Reddit Answers in core search, which must cite threads, respect removals and visibility, and be moderated as the platform's own speech (AI on User-Generated Platforms).
AI crawler blocking: refusing unlicensed AI collection at the edge; Cloudflare made it its default on July 1, 2025 unless crawlers pay, so crawler policy became a CDN setting (AI on User-Generated Platforms).
AI label: a mark on content saying it was AI-generated or altered, set by the uploader's declaration, by detection, from provenance or after review; detected and reviewed labels are moderation decisions with notice and appeal (AI on User-Generated Platforms).
AI training preference: a user's dated choice to allow or opt out of third-party AI use of their content, read by licensed exports at export time and propagated to partners when it changes (AI on User-Generated Platforms).
Article 50 (EU AI Act): the AI Act's transparency article, applying since August 2, 2026, that requires deepfake and public-interest text disclosure by deployers, machine-readable marking by providers, and chatbot disclosure (AI on User-Generated Platforms).
Booked and served clocks: the two dates on every marketplace transaction, when demand happened (what gross booking value counts) and when the stay or trip happened (what revenue counts) (Operating Metrics).
Cell: one of many smaller search clusters, Discord's replacement for two huge Elasticsearch clusters, so the biggest communities can get dedicated indices (Platform Architecture).
Chatbot disclosure: the AI Act duty (Article 50(1)) to tell people they're talking to an AI unless it's obvious, which reaches AI assistants and AI accounts that converse with users (AI on User-Generated Platforms).
Classifier policy: an effective-dated row holding the threshold, target precision and measured precision for one policy category and automated action, with the evaluation that justified it and its approver (AI on User-Generated Platforms).
Community health: active communities, communities with an active moderator, and moderator actions per moderator; Reddit banned 605,570 communities in the second half of 2025, mostly for being unmoderated or spam (Operating Metrics).
Community move: relocating a community that outgrew its shard or cell through copy, catch-up from the event log, a brief write pause and cutover, keeping the old copy until reconciliation passes (Platform Architecture).
Community placement: a row with history recording where a community's partitioned data lives, on a shared or dedicated tier, which the router reads and a legal or residency audit can query by date (Platform Architecture).
Concentration: how much content comes from the top 1% of creators and how much consumption goes to it, both a dependency risk and a moderation risk (Operating Metrics).
Content tombstone: the row that outlives a removed item, holding its id, kind, community, coarse public reason, date and status code but no content, which the serving path and CDN read to answer 404, 410 or 451 (Migrations, Purges & Shutdowns).
Country exit: a shutdown with a border, as Imgur's UK block and Twitch's Korea closure were: scope set as a service-wide geo restriction, rights requests kept open, money settled, embeds and APIs covered and records kept (Migrations, Purges & Shutdowns).
Creators as a share of actives: accounts that posted, commented, uploaded, streamed or listed divided by actives, where a small change is a large change in supply (Operating Metrics).
Data export: a user's re-authenticated, resumable and expiring copy of their data, with originals and history, recording what was excluded, such as others' content or data under a nondisclosure order (Migrations, Purges & Shutdowns).
Data portability (GDPR Article 20): the right to personal data the user provided, processed on consent or contract by automated means, in a structured, machine-readable format, with direct transfer where technically feasible and without harming others' rights (Migrations, Purges & Shutdowns).
Data residency: processing a region's users' data in that region, with the controller per region, a placement property of accounts and content recorded alongside community placement (Platform Architecture).
Data Transfer Initiative: a nonprofit since 2023, grown from the 2018 Data Transfer Project, that builds open-source tools and schemas for moving data between services (Migrations, Purges & Shutdowns).
DAUq (daily active uniques): Reddit's audience metric, a unique identifier that visited a page or opened an app at least once in 24 hours, including logged-out traffic; WAUq is the seven-day version (Operating Metrics).
Declared automation: an app, bot or AI agent account labeled as such everywhere it speaks, with rate limits and permissions fitted to automation; undeclared automation is inauthentic behavior (AI on User-Generated Platforms).
Dedicated tier: the placement for communities that outgrow shared resources, the "Big Freaking Guild" move made as a data change triggered by thresholds on members, messages or index size (Platform Architecture).
Deepfake: in the AI Act, image, audio or video content that a deployer must disclose as artificially generated or manipulated, with a lighter duty for evidently artistic, satirical or fictional work (AI on User-Generated Platforms).
Deletion order: the published rule for which content goes first under a cap or purge (oldest first, least viewed first, or the user's choice); least viewed minimizes broken links (Migrations, Purges & Shutdowns).
Deployer and provider (AI Act): the two roles a platform can hold under Article 50: deployer of AI that generates content (disclose deepfakes) and provider of a generative system (mark outputs in a machine-readable format) (AI on User-Generated Platforms).
Derived store: a search index, feed cache or timeline built from events, the way a platform partitioned by community answers queries that cross communities without scatter-gathering (Platform Architecture).
Edit and delete race: a concurrent edit and delete under last-write-wins that leaves rows without an author, which every store that merges writes needs a rule for (Platform Architecture).
Event spine: the event log every derived system reads (search, feeds, notifications, payouts, metrics, federation), such as Reddit's Kafka with more than 500 brokers (Platform Architecture).
Evidence snapshot: the moderation service's own copy of content as it was judged, kept after edits and deletions under stricter access and retention than the content store (Platform Architecture).
Exposure metric: a measure of how much violating content users actually saw, such as prevalence, violative view rate or reach before removal, the only kind of trust and safety number that says whether users are safer (Operating Metrics).
Fan-out: the multiplication of one write into many deliveries, such as a message to a large server or a live chat line to a big audience, the main cost of real-time features (Platform Architecture).
Fill rate: booked nights over available nights by market and date, which shows where demand exceeds supply (Operating Metrics).
Frozen period: a published or payout-deciding metric value that is fixed once released, corrected only by a restatement row that supersedes it (Operating Metrics).
GMV and GMS: gross merchandise value (eBay's term) and gross merchandise sales (Etsy's), the goods marketplaces' volume measures from which take rate is computed (Operating Metrics).
Gross booking value (GBV): the value of bookings a marketplace counts at booking, adjusted for cancellations and alterations; Airbnb reported $91.3 billion for 2025 (Operating Metrics).
Hot partition: a partition carrying far more load than others because one community, channel or stream is suddenly busy, the defining skew problem of user-generated workloads (Platform Architecture).
Inactive account policy: deleting accounts unused for a period after notice, as Google did for personal accounts unused for two years, with several notices to two addresses over months (Migrations, Purges & Shutdowns).
Link rot: references across the web that break when content is removed, such as Imgur embeds in old Reddit threads; the platform can't prevent it but controls what the URL says afterwards (Migrations, Purges & Shutdowns).
Liquidity: the chance that a search turns into a transaction, measured as search to booking, acceptance, fill rate and time to first booking; not published by the platforms but what operators run on (Operating Metrics).
Logged-out user: a visitor without an account, counted in Reddit's DAUq, which needs a stable anonymous identifier and a written deduplication method because counting such traffic is imperfect (Operating Metrics).
Machine-readable marking: the AI Act duty (Article 50(2)) on generative system providers to mark outputs so they're detectable as artificially generated; systems already on the market before August 2, 2026 have until December 2, 2026 (AI on User-Generated Platforms).
MAU (monthly active users): the audience unit of a discovery product such as Pinterest, which counts authenticated users active in a 30-day window (Operating Metrics).
Media provenance: a row read from the original upload at ingest (digital source type, C2PA validation result, signer) that labels every variant at serving time whatever the image pipeline stripped (AI on User-Generated Platforms).
Metric definition: one versioned definition per metric (unit, population, exclusions such as bots, clock, formula and history policy) that every report reads, so a published figure can be reproduced from its version years later (Operating Metrics).
Modular monolith: the playbook's starting shape, split into services only when a part needs its own scaling or team, with one owner for every piece of data (Platform Architecture).
Nights and seats booked: Airbnb's volume unit (533 million in 2025), counted at booking and adjusted for cancellations and alterations (Operating Metrics).
Partition key: the field data is split by; on a user-generated platform the community (server, subreddit, channel), because reads, permissions and moderation concentrate there (Platform Architecture).
Payout-linked metric: a number that decides money or status (watch hours toward partner thresholds, subscriber counts, a host's response rate), given versioned definitions, stamped outputs, frozen periods and adjustments (Operating Metrics).
Policy-driven purge: a bulk moderation or retention decision applied to a population defined by a rule, for policy, security or cost reasons, run in announced, throttled, reversible stages (Migrations, Purges & Shutdowns).
Pre-send filter: a moderation check on real-time surfaces (chat, live streams) with a tight time budget, such as the 200 milliseconds Amazon IVS gives its chat review handler before a fallback applies (Platform Architecture).
Prevalence sample: one sampled view, labeled with the policy version and carrying its stratum weight, from which prevalence intervals and classifier precision and recall are computed (Operating Metrics).
Process metric: a measure of how well moderation works (proactive rate, time to action, appeal overturn rate, report actionability), as distinct from volume and exposure (Operating Metrics).
Profile move (Mastodon): redirecting followers to a new account after the user sets an alias on it; posts don't move, follows and blocks move by CSV, and another move waits 30 days (Migrations, Purges & Shutdowns).
Purge policy: a dated bulk removal rule with its versioned population query, reason, optional intermediate state and approver, whose batches are recorded as purge runs that can pause and resume (Migrations, Purges & Shutdowns).
Purge population: the set of items a purge targets, defined as a versioned query and counted (by community and referrer) before announcement, because the count shows how much of the web will break (Migrations, Purges & Shutdowns).
Removal propagation: delivering content.removed to every derived store (search, feeds, notifications, AI answer indexes) on a latency target, a moderation feature rather than plumbing (Platform Architecture).
Response and reach: the share of new posts that get a reply, vote or view within a day, the cold-start metric for creators (Operating Metrics).
Restatement: a correction to a published or payout number, recorded as a new row that supersedes the old one and published as such, never a quiet change (Operating Metrics).
Service sunset: ending a feature, service, API version or country as a dated state machine (announced, frozen, read-only, closed, deleted, tombstoned) that users, support and integrations can read (Migrations, Purges & Shutdowns).
Serving by jurisdiction: carrying the viewer's jurisdiction on every request (network edge, refined by account settings and verified age) and evaluating age rules, geographic restrictions and consent from cached, versioned rule data (Platform Architecture).
Skew: the concentration of activity in a few communities, posts or streams, which moves as content goes viral, so a quiet partition can become the hottest in minutes (Platform Architecture).
Tap compare: sending a share of live traffic to a new service and comparing its responses with the old one's while users still get the old responses, as Reddit did moving comments to Go (Platform Architecture).
Time bucket: a time window in a partition key, such as Discord's roughly ten-day buckets per channel, that spreads one channel's history so no partition grows without bound (Platform Architecture).
Tombstone (database): a delete marker in stores like Cassandra; Discord found millions of them in one channel caused ten-second garbage collection pauses, which is why deletes and purges are load (Platform Architecture).
Unit cost: cost per viewer-hour, stored file, delivered image, moderated item or active user, allocated by community and country and tied to the product decision that drives it (Operating Metrics).
Vendor adapter: the platform-owned boundary around a vendor, designed with a latency budget, a failure mode (fail closed for child-safety scanning) and a record of the data it received (Platform Architecture).
Violative View Rate: Snap's exposure metric, the share of Snap and Story views that were of violating content, about 0.01% in the second half of 2025 (Operating Metrics).

410 Gone: the status a removed item's URL answers when it was removed for policy, deleted by its author or purged, with a coarse public reason in the body (Migrations, Purges & Shutdowns).
Acceptance rate: the share of booking requests hosts accept, with median response time and the share that expire; a request-to-book marketplace with a low rate fails guests even when search converts (Operating Metrics).
Active supply: the creators, streamers, sellers, hosts or listings active in a period, the leading indicator for creator and marketplace businesses (Operating Metrics).
Activity fact: one row per identity (account or anonymous identifier) per day it was active, from which DAU, DAUq-style counts, MAU and the DSA's EU recipients are all different queries (Operating Metrics).
AI answers: a model answering questions over the platform's own corpus, such as Reddit Answers in core search, which must cite threads, respect removals and visibility, and be moderated as the platform's own speech (AI on User-Generated Platforms).
AI crawler blocking: refusing unlicensed AI collection at the edge; Cloudflare made it its default on July 1, 2025 unless crawlers pay, so crawler policy became a CDN setting (AI on User-Generated Platforms).
AI label: a mark on content saying it was AI-generated or altered, set by the uploader's declaration, by detection, from provenance or after review; detected and reviewed labels are moderation decisions with notice and appeal (AI on User-Generated Platforms).
AI training preference: a user's dated choice to allow or opt out of third-party AI use of their content, read by licensed exports at export time and propagated to partners when it changes (AI on User-Generated Platforms).
Article 50 (EU AI Act): the AI Act's transparency article, applying since August 2, 2026, that requires deepfake and public-interest text disclosure by deployers, machine-readable marking by providers, and chatbot disclosure (AI on User-Generated Platforms).
Booked and served clocks: the two dates on every marketplace transaction, when demand happened (what gross booking value counts) and when the stay or trip happened (what revenue counts) (Operating Metrics).
Cell: one of many smaller search clusters, Discord's replacement for two huge Elasticsearch clusters, so the biggest communities can get dedicated indices (Platform Architecture).
Chatbot disclosure: the AI Act duty (Article 50(1)) to tell people they're talking to an AI unless it's obvious, which reaches AI assistants and AI accounts that converse with users (AI on User-Generated Platforms).
Classifier policy: an effective-dated row holding the threshold, target precision and measured precision for one policy category and automated action, with the evaluation that justified it and its approver (AI on User-Generated Platforms).
Community health: active communities, communities with an active moderator, and moderator actions per moderator; Reddit banned 605,570 communities in the second half of 2025, mostly for being unmoderated or spam (Operating Metrics).
Community move: relocating a community that outgrew its shard or cell through copy, catch-up from the event log, a brief write pause and cutover, keeping the old copy until reconciliation passes (Platform Architecture).
Community placement: a row with history recording where a community's partitioned data lives, on a shared or dedicated tier, which the router reads and a legal or residency audit can query by date (Platform Architecture).
Concentration: how much content comes from the top 1% of creators and how much consumption goes to it, both a dependency risk and a moderation risk (Operating Metrics).
Content tombstone: the row that outlives a removed item, holding its id, kind, community, coarse public reason, date and status code but no content, which the serving path and CDN read to answer 404, 410 or 451 (Migrations, Purges & Shutdowns).
Country exit: a shutdown with a border, as Imgur's UK block and Twitch's Korea closure were: scope set as a service-wide geo restriction, rights requests kept open, money settled, embeds and APIs covered and records kept (Migrations, Purges & Shutdowns).
Creators as a share of actives: accounts that posted, commented, uploaded, streamed or listed divided by actives, where a small change is a large change in supply (Operating Metrics).
Data export: a user's re-authenticated, resumable and expiring copy of their data, with originals and history, recording what was excluded, such as others' content or data under a nondisclosure order (Migrations, Purges & Shutdowns).
Data portability (GDPR Article 20): the right to personal data the user provided, processed on consent or contract by automated means, in a structured, machine-readable format, with direct transfer where technically feasible and without harming others' rights (Migrations, Purges & Shutdowns).
Data residency: processing a region's users' data in that region, with the controller per region, a placement property of accounts and content recorded alongside community placement (Platform Architecture).
Data Transfer Initiative: a nonprofit since 2023, grown from the 2018 Data Transfer Project, that builds open-source tools and schemas for moving data between services (Migrations, Purges & Shutdowns).
DAUq (daily active uniques): Reddit's audience metric, a unique identifier that visited a page or opened an app at least once in 24 hours, including logged-out traffic; WAUq is the seven-day version (Operating Metrics).
Declared automation: an app, bot or AI agent account labeled as such everywhere it speaks, with rate limits and permissions fitted to automation; undeclared automation is inauthentic behavior (AI on User-Generated Platforms).
Dedicated tier: the placement for communities that outgrow shared resources, the "Big Freaking Guild" move made as a data change triggered by thresholds on members, messages or index size (Platform Architecture).
Deepfake: in the AI Act, image, audio or video content that a deployer must disclose as artificially generated or manipulated, with a lighter duty for evidently artistic, satirical or fictional work (AI on User-Generated Platforms).
Deletion order: the published rule for which content goes first under a cap or purge (oldest first, least viewed first, or the user's choice); least viewed minimizes broken links (Migrations, Purges & Shutdowns).
Deployer and provider (AI Act): the two roles a platform can hold under Article 50: deployer of AI that generates content (disclose deepfakes) and provider of a generative system (mark outputs in a machine-readable format) (AI on User-Generated Platforms).
Derived store: a search index, feed cache or timeline built from events, the way a platform partitioned by community answers queries that cross communities without scatter-gathering (Platform Architecture).
Edit and delete race: a concurrent edit and delete under last-write-wins that leaves rows without an author, which every store that merges writes needs a rule for (Platform Architecture).
Event spine: the event log every derived system reads (search, feeds, notifications, payouts, metrics, federation), such as Reddit's Kafka with more than 500 brokers (Platform Architecture).
Evidence snapshot: the moderation service's own copy of content as it was judged, kept after edits and deletions under stricter access and retention than the content store (Platform Architecture).
Exposure metric: a measure of how much violating content users actually saw, such as prevalence, violative view rate or reach before removal, the only kind of trust and safety number that says whether users are safer (Operating Metrics).
Fan-out: the multiplication of one write into many deliveries, such as a message to a large server or a live chat line to a big audience, the main cost of real-time features (Platform Architecture).
Fill rate: booked nights over available nights by market and date, which shows where demand exceeds supply (Operating Metrics).
Frozen period: a published or payout-deciding metric value that is fixed once released, corrected only by a restatement row that supersedes it (Operating Metrics).
GMV and GMS: gross merchandise value (eBay's term) and gross merchandise sales (Etsy's), the goods marketplaces' volume measures from which take rate is computed (Operating Metrics).
Gross booking value (GBV): the value of bookings a marketplace counts at booking, adjusted for cancellations and alterations; Airbnb reported $91.3 billion for 2025 (Operating Metrics).
Hot partition: a partition carrying far more load than others because one community, channel or stream is suddenly busy, the defining skew problem of user-generated workloads (Platform Architecture).
Inactive account policy: deleting accounts unused for a period after notice, as Google did for personal accounts unused for two years, with several notices to two addresses over months (Migrations, Purges & Shutdowns).
Link rot: references across the web that break when content is removed, such as Imgur embeds in old Reddit threads; the platform can't prevent it but controls what the URL says afterwards (Migrations, Purges & Shutdowns).
Liquidity: the chance that a search turns into a transaction, measured as search to booking, acceptance, fill rate and time to first booking; not published by the platforms but what operators run on (Operating Metrics).
Logged-out user: a visitor without an account, counted in Reddit's DAUq, which needs a stable anonymous identifier and a written deduplication method because counting such traffic is imperfect (Operating Metrics).
Machine-readable marking: the AI Act duty (Article 50(2)) on generative system providers to mark outputs so they're detectable as artificially generated; systems already on the market before August 2, 2026 have until December 2, 2026 (AI on User-Generated Platforms).
MAU (monthly active users): the audience unit of a discovery product such as Pinterest, which counts authenticated users active in a 30-day window (Operating Metrics).
Media provenance: a row read from the original upload at ingest (digital source type, C2PA validation result, signer) that labels every variant at serving time whatever the image pipeline stripped (AI on User-Generated Platforms).
Metric definition: one versioned definition per metric (unit, population, exclusions such as bots, clock, formula and history policy) that every report reads, so a published figure can be reproduced from its version years later (Operating Metrics).
Modular monolith: the playbook's starting shape, split into services only when a part needs its own scaling or team, with one owner for every piece of data (Platform Architecture).
Nights and seats booked: Airbnb's volume unit (533 million in 2025), counted at booking and adjusted for cancellations and alterations (Operating Metrics).
Partition key: the field data is split by; on a user-generated platform the community (server, subreddit, channel), because reads, permissions and moderation concentrate there (Platform Architecture).
Payout-linked metric: a number that decides money or status (watch hours toward partner thresholds, subscriber counts, a host's response rate), given versioned definitions, stamped outputs, frozen periods and adjustments (Operating Metrics).
Policy-driven purge: a bulk moderation or retention decision applied to a population defined by a rule, for policy, security or cost reasons, run in announced, throttled, reversible stages (Migrations, Purges & Shutdowns).
Pre-send filter: a moderation check on real-time surfaces (chat, live streams) with a tight time budget, such as the 200 milliseconds Amazon IVS gives its chat review handler before a fallback applies (Platform Architecture).
Prevalence sample: one sampled view, labeled with the policy version and carrying its stratum weight, from which prevalence intervals and classifier precision and recall are computed (Operating Metrics).
Process metric: a measure of how well moderation works (proactive rate, time to action, appeal overturn rate, report actionability), as distinct from volume and exposure (Operating Metrics).
Profile move (Mastodon): redirecting followers to a new account after the user sets an alias on it; posts don't move, follows and blocks move by CSV, and another move waits 30 days (Migrations, Purges & Shutdowns).
Purge policy: a dated bulk removal rule with its versioned population query, reason, optional intermediate state and approver, whose batches are recorded as purge runs that can pause and resume (Migrations, Purges & Shutdowns).
Purge population: the set of items a purge targets, defined as a versioned query and counted (by community and referrer) before announcement, because the count shows how much of the web will break (Migrations, Purges & Shutdowns).
Removal propagation: delivering content.removed to every derived store (search, feeds, notifications, AI answer indexes) on a latency target, a moderation feature rather than plumbing (Platform Architecture).
Response and reach: the share of new posts that get a reply, vote or view within a day, the cold-start metric for creators (Operating Metrics).
Restatement: a correction to a published or payout number, recorded as a new row that supersedes the old one and published as such, never a quiet change (Operating Metrics).
Service sunset: ending a feature, service, API version or country as a dated state machine (announced, frozen, read-only, closed, deleted, tombstoned) that users, support and integrations can read (Migrations, Purges & Shutdowns).
Serving by jurisdiction: carrying the viewer's jurisdiction on every request (network edge, refined by account settings and verified age) and evaluating age rules, geographic restrictions and consent from cached, versioned rule data (Platform Architecture).
Skew: the concentration of activity in a few communities, posts or streams, which moves as content goes viral, so a quiet partition can become the hottest in minutes (Platform Architecture).
Tap compare: sending a share of live traffic to a new service and comparing its responses with the old one's while users still get the old responses, as Reddit did moving comments to Go (Platform Architecture).
Time bucket: a time window in a partition key, such as Discord's roughly ten-day buckets per channel, that spreads one channel's history so no partition grows without bound (Platform Architecture).
Tombstone (database): a delete marker in stores like Cassandra; Discord found millions of them in one channel caused ten-second garbage collection pauses, which is why deletes and purges are load (Platform Architecture).
Unit cost: cost per viewer-hour, stored file, delivered image, moderated item or active user, allocated by community and country and tied to the product decision that drives it (Operating Metrics).
Vendor adapter: the platform-owned boundary around a vendor, designed with a latency budget, a failure mode (fail closed for child-safety scanning) and a record of the data it received (Platform Architecture).
Violative View Rate: Snap's exposure metric, the share of Snap and Story views that were of violating content, about 0.01% in the second half of 2025 (Operating Metrics).