Open API

These days, APIs are especially important because they dictate

-        How developers can create new apps which can tap into
          
          - > Big Web services,
        
         -  > Social networks like  Facebook, Pinterest, Twitter
       
         -  > Utilities like Google Maps or Dropbox


Open APIs are published on the Internet and shared freely.

A startup software company, for example might publish a series of APIs to encourage third-party developers in vertical industries to be innovative and figure out new ways to use the startup’s software product.

In theory, it’s a win-win business arrangement.

The startup gets to expand their company’s user base without having to spend any money to develop niche industry software -- and they still get to keep their source code proprietary.

In one sense, then, APIs are great time savers.  They also offer user convenience in many cases;

Example 1:

Facebook incorporated an open API into its business model.

Facebook users undoubtedly appreciate the ability to sign into many apps and Web sites using their Facebook ID—a feature that relies upon Facebook APIs to work.

Example 2:

When you search for nearby restaurants in the Yelp app for Android, for instance,
it will plot their locations on Google Maps instead of creating its own maps.

Its happening through Via the Google Maps API, the Yelp app passes the information it wants plotted—restaurant addresses, say, along with the Yelp star rating and more—
to an internal Google Maps function that then returns a Map object with restaurant pins in it at the proper locations.

Which Yelp can then display inside its app. (On iOS, Yelp taps Apple's Maps API for the same purpose.)

Example 3:

In lot of web pages, you can see  icons to share this article on Facebook, Google+, Twitter, LinkedIn or Reddit. These are just links that call on the APIs associated with each of those services to allow users to Tweet or post about an article without leaving the site itself