What is AJAX?

AJAX = Asynchronous JavaScript and XML.

AJAX is a technique for creating fast and dynamic web pages.
AJAX is not a new programming language, but a new way to use existing standards.

AJAX is the art of exchanging data with a server.
AJAX allows web pages to be updated asynchronously by exchanging small amounts of data with the server behind the scenes and update parts of a web page, without reloading the whole page.

Note : Classic web pages, (which do not use AJAX) must reload the entire page if the content should change.

Useful Link : http://www.w3schools.com/ajax/ajax_intro.asp