API (Application Program Interface)
API is the abbreviation for Application Program Interface, which is a set of routines, protocols, and tools for building software applications. A good API makes it easier to develop a program by providing all the building blocks. A programmer puts the blocks together.
Most operating environments, such as MS Windows, provide an API so that programmers can write applications consistent with the operating environment. Although APIs are designed for programmers, they are ultimately of advantage to users because they guarantee that all programs using a common API will have similar interfaces. This makes it easier for users to learn new programs.