Application Programming Interface (API) is a set of tools and standards that allows two applications to talk to each other. The API defines a common language that both applications understand. A developer can use it to create software that will be compatible with many different applications or devices. An excellent example of an API is Google maps. When you open your web browser and type in a location, Google Maps displays the map of that location with all its relevant information like restaurants, hotels and other businesses nearby. The big difference between Google Maps and any other mapping service is that it uses an open API which means anyone can build on top of it.
Benefits: An application programming interface allows developers to create new applications based on existing code. The advantage for users is that they do not need to learn new languages or technologies to use the new application. For example, if you want to create a new app that works with Facebook, all you need is an account with Facebook and an understanding of RESTful APIs. It’s also easier for developers since they don't have to worry about learning new languages or technologies to use these services.