AJAX = Asynchronous JavaScript and XML.
AJAX is a technique for creating fast dynamic web pages.
By exchanging small amounts of data with the server behind the scenes, AJAX can make asynchronous page updates. This means you can , for a certain part of the page is updated without reloading the entire page .
Traditional web page (do not use AJAX) If you need to update the entire page surface content, essential overloaded.
There are many applications that use AJAX Case: Sina Weibo, Google Maps, happy, and so on.