APi stands for 'application program interface'. API is a tool for programmers to help develop new programs easier. API has a set of routines, protocols, and tools for programmes who are building software applications for most operating systems like MS Windows and Unix. The most useful feature of a API suite is it guarantees all software developers are using the same interfaces and routines. This should mean the programs they develop are more reliable, and with common features it means users can easily understand and learn to use the programs.