Application programming interface (API)
A set of routines, protocols and tools referred to as "building blocks" used in business application software development. A good API makes it easier to develop a program by providing all the building blocks related to functional characteristics of an operating system, which applications need to specify when, for example, interfacing with an operating system (e.g., provided by MS-Windows, different versions of UNIX). A programmer would utilize these APIs in developing applications that can operate effectively and efficiently on the platform chosen.