API word has become so common on the web that you find it everywhere from technical blogs to books. I am sure you have heard about Google Maps API, Facebook Graph API, Twitter API. The defination of an API is -
An application programming interface (API) is a particular set of instructions that programs can follow to communicate with each other. It serves as an interface between different programs and facilitates their interaction, similar to the way the user interface facilitates interaction between humans and computers.
So what does this means? Suppose I am working on a Web Application and I want to use services of other applications on the web. APIs provides an interface to talk to other applications with our application. For example, Google Maps API allows to Access information about establishments, geographic locations, or prominent points of interest. Facebook Graph API allows us to extend the features provided by facebook to suit our needs, Ex - To Calculate number of likes that are common to a post and page, Mass Responding to Posts on Your Timeline.
Almost all of the popular services on the web have their APIs available to the developers so that they can build their applications on top it.
Some of the most popular APIs are :
APIs allows developers to integrate remote applications with their own applications. Thus reducing the efforts to write every part of application from scratch. For example, when we purchase something from a website by entering our credit card information, the website uses API to connect to remote application to check whether the information provided by you is correct. Once payment is confirmed, the remote application sends a response to the website that the payment is received and the product can be sold.
So, there are number of APIs available on the web waiting for you to use them. Find APIs according to your needs and integrate them in your next Cool Application.