Application Programming InterfaceApplication program interface (API), is a set of routines, protocols, and tools for building software applications. The API specifies how software components should interact and are used when programming graphical user interface (GUI) components.
A good API makes it easier to develop a program by providing all the building blocks. A programmer then puts the blocks together. When you copy and paste text from one application to another, it is the API that allows that to work.
The API allows programmers to use predefined functions to interact with the operating system, instead of writing them from scratch.
by Software Testing Company