An Application Programming Interface (API) is an interface between one web application and another so they can make use of their services, resources and interact. On a simple web site API integration can be useful with Login authentication to Social and Search Engine marketing . It can also facilitate the use and synchronization of (external) data. Different web site tools can have different APIs, and while some might be very basic, others might allow you to use many functions of the email platform. The use of APIs and API integration makes it possible to automate specific tasks.
Few famous apis include Google map API, facebook api, twitter api.