# Running the Platform Glossary

> 37 terms from the Investing & Digital Assets book's Running the Platform part, each defined in a line and linked to the chapter that explains it.

- **Account shard:** one slice of a broker's or exchange's accounts with its own application servers, database and deploy pipeline, so a failure or a release touches only that slice ([Trading Platform Architecture](https://www.syntaqx.com/books/investing-and-digital-assets/trading-platform-architecture#sharding-by-account)).
- **Account shard mapping:** the stored record of which shard holds an account, read by the router and cached, so an account can move without rehashing every other ([Trading Platform Architecture](https://www.syntaqx.com/books/investing-and-digital-assets/trading-platform-architecture#sharding-by-account)).
- **Active brokerage account:** Schwab's count of brokerage accounts with activity in the preceding 270 days ([Investing & Digital Assets Metrics](https://www.syntaqx.com/books/investing-and-digital-assets/investing-metrics#how-the-companies-report)).
- **Agent mandate:** the customer's stored authorization for a software agent trading an account: instruments, order types, per-order and daily limits, hours and expiry, checked by the platform on every order ([AI in Investing](https://www.syntaqx.com/books/investing-and-digital-assets/ai-in-investing#agents-that-trade-and-hold-wallets)).
- **AI washing:** claiming in marketing or filings to use AI that a firm doesn't use as described; the SEC's 2024 actions against Delphia and Global Predictions ([AI in Investing](https://www.syntaqx.com/books/investing-and-digital-assets/ai-in-investing#ai-washing)).
- **ARPU (broker):** total revenue over the average of funded customers at the end of the period and the prior period, annualized in quarterly releases ([Investing & Digital Assets Metrics](https://www.syntaqx.com/books/investing-and-digital-assets/investing-metrics#revenue-per-customer)).
- **Brokerage conversion:** moving accounts in bulk from one platform or firm to another without each customer's transfer instruction, in batches with a freeze, load, reconciliation and go decision ([Conversions, Shutdowns & Distributions](https://www.syntaqx.com/books/investing-and-digital-assets/conversions-and-shutdowns#brokerage-conversions)).
- **Business continuity plan (FINRA 4370):** a broker-dealer's written plan for meeting obligations to customers through a significant business disruption, covering at least ten listed areas including mission critical systems and alternate customer communications ([Peak Days, Outages & Resilience](https://www.syntaqx.com/books/investing-and-digital-assets/peak-days-and-outages#finra-rule-4370-the-continuity-plan)).
- **Control total:** a sum or count taken from the source and the target of a migration at one level (accounts, positions, shares, cash, lots, adjusted basis) and compared before going live ([Conversions, Shutdowns & Distributions](https://www.syntaqx.com/books/investing-and-digital-assets/conversions-and-shutdowns#worked-numbers-reconciling-one-batch)).
- **Core net new assets:** Schwab's net new client assets before significant one-time flows such as acquisitions ([Investing & Digital Assets Metrics](https://www.syntaqx.com/books/investing-and-digital-assets/investing-metrics#flows)).
- **Covered technology:** in the SEC's withdrawn 2023 proposal, any analytical function that optimizes for, predicts, guides, forecasts or directs investment-related behaviors or outcomes in an investor interaction ([AI in Investing](https://www.syntaqx.com/books/investing-and-digital-assets/ai-in-investing#the-withdrawn-predictive-data-analytics-proposal)).
- **DARTs:** daily average revenue trades, customer orders that generate revenue per trading day, as Interactive Brokers reports them ([Investing & Digital Assets Metrics](https://www.syntaqx.com/books/investing-and-digital-assets/investing-metrics#trading-activity-and-take-rate)).
- **Degraded mode:** a deliberate, scoped state (cancel-only, close-only, read-only, withdrawals paused, a feature off) that the platform enters during an incident, with a runbook and a customer message ([Peak Days, Outages & Resilience](https://www.syntaqx.com/books/investing-and-digital-assets/peak-days-and-outages#load-shedding-and-degraded-modes)).
- **Device binding:** a record that a customer proved a device with a passkey or device key, used as evidence that later instructions from it come from the customer ([Account Security & Fraud](https://www.syntaqx.com/books/investing-and-digital-assets/account-security#device-binding-and-step-up)).
- **Distribution agent:** a firm a bankruptcy estate uses to pay creditors in cash or crypto, such as PayPal and Coinbase in the Celsius case ([Conversions, Shutdowns & Distributions](https://www.syntaqx.com/books/investing-and-digital-assets/conversions-and-shutdowns#bankruptcies-and-distributions)).
- **Entity partition:** the region, database cluster and shards that hold one legal entity's data, recorded as a row so the entity can be moved, isolated or wound down ([Trading Platform Architecture](https://www.syntaqx.com/books/investing-and-digital-assets/trading-platform-architecture#multi-entity-design)).
- **Escheatment:** turning unclaimed money over to the state after a dormancy period ([Conversions, Shutdowns & Distributions](https://www.syntaqx.com/books/investing-and-digital-assets/conversions-and-shutdowns#unclaimed-property)).
- **Funded customer:** Robinhood's count of unique people with an account at any of its entities that had a positive balance (excluding firm-granted promotions) or a transaction in the past 45 days ([Investing & Digital Assets Metrics](https://www.syntaqx.com/books/investing-and-digital-assets/investing-metrics#customers-and-accounts)).
- **Indication of interest (unclaimed property):** an owner's act that restarts the dormancy clock, such as a communication about the property or owner-directed activity in the account, as Delaware's law lists them ([Conversions, Shutdowns & Distributions](https://www.syntaqx.com/books/investing-and-digital-assets/conversions-and-shutdowns#unclaimed-property)).
- **Invariant check:** a stored query that must return no rows (an entry that doesn't balance, a ledger-to-chain difference, a negative balance without credit), run on a schedule with its result kept ([Trading Platform Architecture](https://www.syntaqx.com/books/investing-and-digital-assets/trading-platform-architecture#invariants-checked-continuously)).
- **Market exit:** a platform stopping service to a country or state, run as a sequence of states from notice to close-only, withdraw-only and final disposition ([Conversions, Shutdowns & Distributions](https://www.syntaqx.com/books/investing-and-digital-assets/conversions-and-shutdowns#exiting-a-market)).
- **Meaningful wallet:** Circle's count of on-chain wallets holding at least $10 of USDC ([Investing & Digital Assets Metrics](https://www.syntaqx.com/books/investing-and-digital-assets/investing-metrics#stablecoin-supply-and-reserve-income)).
- **Mission critical system:** under FINRA 4370, any system needed for prompt and accurate processing of securities transactions, from order taking and execution to access to customer accounts and delivery of funds and securities ([Peak Days, Outages & Resilience](https://www.syntaqx.com/books/investing-and-digital-assets/peak-days-and-outages#finra-rule-4370-the-continuity-plan)).
- **Monthly transacting user (MTU):** Coinbase's count of consumers who actively or passively transacted at least once in a rolling 28 days ([Investing & Digital Assets Metrics](https://www.syntaqx.com/books/investing-and-digital-assets/investing-metrics#how-the-companies-report)).
- **Negative response letter:** a notice telling customers their accounts will move in a bulk transfer unless they object within at least 30 days, accepted by FINRA in listed circumstances ([Conversions, Shutdowns & Distributions](https://www.syntaqx.com/books/investing-and-digital-assets/conversions-and-shutdowns#brokerage-conversions)).
- **Net deposits:** money and assets customers brought in, plus dividends, interest, staking rewards and promotions, less withdrawals, transfers out, interest and subscription fees charged; distinct from performance external flows ([Investing & Digital Assets Metrics](https://www.syntaqx.com/books/investing-and-digital-assets/investing-metrics#flows)).
- **Outage compensation:** a payment to a customer for a trade an outage prevented, computed from a logged attempt, the price at the attempt and the first reasonable opportunity after recovery ([Peak Days, Outages & Resilience](https://www.syntaqx.com/books/investing-and-digital-assets/peak-days-and-outages#paying-for-outages)).
- **Posting service:** the one writer of journal entries, holds and positions; every other service asks it to move money or assets ([Trading Platform Architecture](https://www.syntaqx.com/books/investing-and-digital-assets/trading-platform-architecture#the-services)).
- **Restitution payment:** money or assets a firm pays a customer for a loss outside a platform security incident, by firm error, voluntary policy, a regulator's order, an award or a settlement ([Account Security & Fraud](https://www.syntaqx.com/books/investing-and-digital-assets/account-security#restitution)).
- **SCI entity:** a self-regulatory organization, an ATS over Regulation SCI's volume thresholds, a plan processor, certain exempt clearing agencies or a competing consolidator, subject to the SEC's systems resilience rule; not a broker-dealer as such ([Peak Days, Outages & Resilience](https://www.syntaqx.com/books/investing-and-digital-assets/peak-days-and-outages#regulation-sci)).
- **SCI event:** a systems disruption, systems compliance issue or systems intrusion at an SCI entity, with corrective action and notice to the SEC immediately and in writing within 24 hours ([Peak Days, Outages & Resilience](https://www.syntaqx.com/books/investing-and-digital-assets/peak-days-and-outages#regulation-sci)).
- **Security change hold:** a withdrawal hold placed when value is sent to a destination added after a password, contact, 2FA or device change, with notice to the contact points that existed before the change ([Account Security & Fraud](https://www.syntaqx.com/books/investing-and-digital-assets/account-security#withdrawal-holds-and-allowlists)).
- **Sequenced input:** an order, fill, deposit or other instruction given a gapless per-account sequence number before it's applied, so the account's state can be replayed in order ([Trading Platform Architecture](https://www.syntaqx.com/books/investing-and-digital-assets/trading-platform-architecture#sequencing-and-the-event-log)).
- **SIM swap:** moving a customer's phone number to an attacker's SIM or carrier to receive their SMS codes; carriers must authenticate and notify under the FCC's 2023 order ([Account Security & Fraud](https://www.syntaqx.com/books/investing-and-digital-assets/account-security#the-attack-paths)).
- **Surge factor:** the multiple of a normal peak a capacity plan is built for, set from the platform's history and public peaks such as Robinhood's 7x in 2020 ([Peak Days, Outages & Resilience](https://www.syntaqx.com/books/investing-and-digital-assets/peak-days-and-outages#capacity-for-a-meme-stock-day)).
- **Take rate:** net revenue over gross volume, in basis points, read with its mix ([Investing & Digital Assets Metrics](https://www.syntaqx.com/books/investing-and-digital-assets/investing-metrics#trading-activity-and-take-rate)).
- **Withdrawal hold:** a stop on one outbound transfer for a stated reason (a new destination, a security change, risk review, a customer lock, a senior investor hold, a legal order), released by a timer, the customer or a reviewer ([Account Security & Fraud](https://www.syntaqx.com/books/investing-and-digital-assets/account-security#withdrawal-holds-and-allowlists)).

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