An application programming interface (API) is an interface in computer science that defines the ways by which an application program may request services from libraries and/or operating systems.[1][2][3] An API determines the vocabulary and calling conventions the programmer should employ to use the services. It may include specifications for routines, data structures, object classes, and protocols used to communicate between the requesting software and the library.
An API may be:
Language-dependent; that is, available only in a given programming language, using the syntax and elements of that language to make the API convenient to use in this context.
Language-independent; that is, written in a way that means it can be called from several programming languages (typically an assembly or C interface). This is a desired feature for a service-style API that is not bound to a given process or system and is available as a remote procedure call.
An API itself is largely abstract in that it specifies an interface and controls the behavior of the objects specified in that interface. The software that provides the functionality described by an API is said to be an implementation of the API. An API is typically defined in terms of the programming language used to build the application. The related term application binary interface (ABI) is a lower level definition concerning details at the assembly language level. For example, the Linux Standard Base is an ABI, while POSIX is an API.
The API initialism may sometimes be used as a reference, not only to the full interface, but also to one function, or even a set of multiple APIs provided by an organization. Thus, the scope of meaning is usually determined by the person or document that communicates the information
