An application-programming interface(API) consists of a set of standards and programming instructions for accessing a Web tool or Web-based software application. Application Program interface is a set of protocols, routines, and tools required for building software applications. An API specifies the way in which the software components should interact. Additionally, APIs are used when the graphical user interface(GUI) components are to be programmed. A good API provides all the building blocks and makes it easier to develop a program. A programmer puts all the building blocks together.
Different types of APIs are available for operating systems, applications or websites. For example, ‘Windows’ has many API sets that are being used by the system hardware and applications i.e. when users copy and paste text from one application to another, it is the API that makes it work. Most of the operating environments, such as MS-Windows also provides APIs which allows the programmers to write applications that are consistent with the operating environment. To read more info – http://bit.ly/2jXcp5P