An API or Application Programming Interface is what different pieces of software use to talk to each other, in the same way that people talk to each other in order to share knowledge. The API is like an auto-translator, a space that takes the information produced by one program and makes sure that it is understood by another.
What is an API
The actual API is the idea — the software code that is written for it is an implementation of this idea. It can be just one or many thousands of references to different functions or actions of a software program which can be “called” or used by another program to get the results it wants. Once this is understood, it allows programs and communities to openly share information with each other, resulting in a better experience for Internet users.
Rather than needing to know how a particular function works, knowing how it behaves once it has been called is of greatest importance to the program doing the calling. Once it is clear how a particular program's information will behave in a variety of circumstances, people can share information successfully between different programs, for example by posting a photo on Flickr and having it automatically appear on Facebook and Twitter.
More Interface, More Fun
Web APIs allow mashups, Web sites or mini-tools that build new functionality and utility on the shoulders of existing Web applications by combining them and adding to them in creative ways. These are also known as badges, widgets or apps, which can then be sold or distributed for free to an eager public. The API is a great way to share information at low risk, because it will only make public the limited information and functions that a company is happy to share.
Utility and Stability Is King
APIs can be written in multiple computer languages, or they can be made to be read no matter what language is calling them. The ones that are successfully adopted by coders will have good documentation, great stability in every computer environment and behave as documented over the long haul.
Better Web Sites with APIs
APIs are available to help people create the kind of service they would like from the Internet. It is much easier to post a status update or promotional offer once, then use APIs to send the information to all the social networking applications that hold a profile for you. APIs can also enhance your Web site, as they help you embed videos or slide shows on to your pages. You can also use APIs that are more interactive; for example, you could add a function that enables price or service comparisons with your closest competitors in real time, or add a map to any address using a Google API.