API key

An application programming interface key (API key) is a code passed in by computer programs calling an API (application programming interface) to identify the calling program, its developer, or its user to the Web site. API keys are used to track and control how the API is being used, for example, to prevent malicious use or abuse of the API (as defined perhaps by terms of service).

The API key often acts as both a unique identifier and a secret token for authentication, and will generally have a set of access rights on the API associated with it.

You can meet API keys in PayPal, Google Maps, Facebook and other services. Such keys are used to embed some service interface into custom websites (social feeds, payment modules, etc).