Application Programming Interface

An Application Programming Interface (often shortened to the acronym, API) is a formal interface specification for a software sub-system. The form of each API will depend on the system in which it is defined. For example, for an API in a programming language, it would be a list of subroutine names, with the arguments for each individual subroutine. For one used over a data network, it would specify the protocol to be used, along with the details (syntax, and semantics) of what information has to be supplied to the entity at the other end, along with the details of what information will be returned.