API
full spelling ： Application Program Interface
API is a set of orders and functions that can be used when software for certain platforms (OS or middleware) are developed, or a set of agreements about procedures on programs to use them. It is hard and wasteful for individual software developers to programme all the function that the software has, so the functions which most software use in common are offered in the form of OS or middleware altogether. Individual developers can create software using the function without programming it only by "summoning" it in accordance with the agreement.