API Key
A secret token identifying and authorizing an application (not a user) when it calls an API.
An API key is a secret token an application includes with its requests to identify and authorize itself to an API. Unlike user auth, it identifies the calling application or project, and is used for access control, rate limiting, and usage metering.
Worked example: a weather app sends its API key on each call; the provider checks the key is valid, applies that key’s rate limit and plan, and bills or blocks accordingly. Gotcha: API keys are bearer secrets — anyone who has the key can use it — so they must never be embedded in client-side or browser code or committed to git, should be scoped and rotatable, and for user-delegated access OAuth (not a shared key) is the right tool; a leaked key is a direct breach.