A set of related functions that a computer programmer uses to obtain some kind of service from another piece of software. Programmers of Windows based applications use the Windows API to create windows, draw text on the screen, access files, and perform all other services provided by Windows. Despite the use of the word application in this term, applications might not be the only software using an API; lower-level software components such as network drivers also have APIs, but these components are not “applications” and are not used directly by applications.