What is an API?

API, originally Advanced Programming Interface but now more commonly known by its near synonym, Application programming interface, is any defined inter-program interface.

An application programming interface (API) is a set of declarations of the functions (or procedures) that an operating system, library or service provides to support requests made by computer programs.

• Language-dependent APIs are available only in a particular programming language. They utilize the syntax and elements of the programming language to make the API convenient to use in this particular context.

• Language-independent APIs are written in a way that means they can be called from several programming languages. This is a desired feature for a service-style API which is not bound to a particular process or system and is available as a remote procedure call.

In short - API Keys allow for one website to speak to another website behind the scenes.  Most often for inventory and accounting purposes.