Application Program Interface API Application Programming Interface Applications Programming Interface <programming> (API, or "application programming interface") The interface (calling conventions) by which an {application program} accesses {operating system} and other services. An API is defined at {source code} level and provides a level of {abstraction} between the application and the {kernel} (or other privileged utilities) to ensure the {portability} of the code. An API can also provide an interface between a {high level language} and lower level utilities and services which were written without consideration for the {calling conventions} supported by compiled languages. In this case, the API's main task may be the translation of parameter lists from one format to another and the interpretation of {call-by-value} and {call-by-reference} arguments in one or both directions. (1995-02-15)