AJAX is a group of interrelated web development methods used on the client-side to create asynchronous web applications. With Ajax, web applications can send data to, and retrieve data from, a server asynchronously (in the background) without interfering with the display and behavior of the existing page. Data is usually retrieved using the
XMLHttpRequest object. Despite the name, the use of XML is not needed (JSON is often used instead), and the requests do not need to be asynchronous.
XMLHttpRequest object provide a method for exchanging data asynchronously between browser and server to avoid full page reloads.