Application programming interface or also known as API’s allow your product or services to talk to another product or service, and they are used to give people access to your data/resources from outside the firewall.It means opening up your product’s data or functionality to other developers internally and externally
Actually we deal with API’s all the time.they are used to integrate website and system with other website and system such as Amazon,twitter,eBAY etc..
Let us take a real life example:
Here is a real-life application programming interface example. You may be familiar with the process of searching flights online. Just like the restaurant, you have a variety of options to choose from, including different cities, departure and return dates, and more.
Let us imagine that you’re booking you are flight on an airline website. You choose a departure city and date, a return city and date, cabin class, as well as other variables. In order to book your flight, you interact with the airline’s website to access their database and see if any seats are available on those dates and what the costs might be.
Most famous API’s:
In one way or another, Google APIs support most modern sites online. From analytics, to the advertising exchange, maps, to Google+ shares, chances are, most sites are using a Google API. Currently, 57 application programming interfaces are available from Google, as well as a number of other developer tools.
Social media APIs are used for multiple reasons. The ability to log into a site using a social media profile (eg facebook)helps users quickly access content, and keep the number of separate accounts and passwords they have to keep track of low.
Infact the ability to instantly share content socially, can be a great boom to app or site engagement, and the ability to look at social media data and key into your true audience is always valuable.
The Data API allows users to integrate their program with YouTube and allow it to perform many of the operations available on the website.
It provides the capability to search for videos, retrieve standard feeds, and see related content. A program can also authenticate as a user to upload videos, modify user playlists, and more.finally youtube application programming interface are the popular API’s after GOOGLE API’s