# REST API flash cards: Freelancer level

15 REST API terms at the Freelancer level, as flash cards.

Updated: September 27, 2026

- [Study these as flash cards](https://www.ask-codey.com/decks/rest-api/4/flash)
- [Play Memory with them](https://www.ask-codey.com/games/memory?category=rest-api&level=4)

## Terms in this deck

- [API Gateway](https://www.ask-codey.com/glossary/api-gateway): A single front door that routes requests to many backend services.
- [Backend for Frontend](https://www.ask-codey.com/glossary/backend-for-frontend): A small server built for one front end, shaping data and holding tokens.
- [Caching Headers](https://www.ask-codey.com/glossary/caching-headers): Headers that say how long a response may be reused.
- [Conditional Request](https://www.ask-codey.com/glossary/conditional-request): A request that only proceeds if the resource is still in the expected state.
- [Content Negotiation](https://www.ask-codey.com/glossary/content-negotiation): The client asks for a format with Accept; the server picks one it supports.
- [Contract Testing](https://www.ask-codey.com/glossary/contract-testing): Checking an API still matches its agreed description.
- [ETag](https://www.ask-codey.com/glossary/etag): A version fingerprint that lets clients skip downloading unchanged data.
- [Idempotency Key](https://www.ask-codey.com/glossary/idempotency-key): A unique value that stops a retried POST from happening twice.
- [Long-Running Operation](https://www.ask-codey.com/glossary/long-running-operation): Answering 202 at once and letting the client poll a status URL.
- [OAuth 2.0](https://www.ask-codey.com/glossary/oauth-2-0): A standard for granting apps limited access via tokens instead of passwords.
- [OpenID Connect](https://www.ask-codey.com/glossary/openid-connect): Sign-in built on OAuth 2.0; used by "Sign in with Google".
- [Preflight Request](https://www.ask-codey.com/glossary/preflight-request): The OPTIONS check a browser sends before some cross-origin requests.
- [Rate Limiting](https://www.ask-codey.com/glossary/rate-limiting): Capping how many requests a client can send in a period.
- [Refresh Token](https://www.ask-codey.com/glossary/refresh-token): A long-lived token used to get new short-lived access tokens.
- [Webhook](https://www.ask-codey.com/glossary/webhook): An HTTP call a service sends to your URL when something happens.

[Read them in the glossary](https://www.ask-codey.com/glossary/subjects/rest-api/freelancer)

Source: https://www.ask-codey.com/decks/rest-api/freelancer