What is AJAX
AJAX is an Jquery API which is use to send and receive data asynchronously means without reloading the entire web page.
With Ajax we can transfer some set of data from web page to the server.
We can update the part of our web page without refreshing the entire page using AJAX.
Where AJAX used
There are so many web sites which are using Ajax API to get the data asynchronously like google map, youtube, Facebook, Google Search Box.
Let me explain how Google map works, when you will type any location name in google map Search box then google starts fetching that location from google server without refreshing any page.
One of the most popular example of Ajax is when you type any thing in google search box then google will display some recommendation text that is totally based on Ajax call.