AJAX stands for Asynchronous JavaScript and XML. AJAX is the technology for creating better, faster, and more interactive web applications with the help of HTML, CSS, and JavaScript.

With AJAX, when you hit submit, JavaScript will make a request to the server, interpret the results, and update the current screen. In the purest sense, the user would never know that anything was even transmitted to the server.

A user can continue to use the application while the client program requests information from the server in the background.

It is mostly used in Rich Internet Applications(RIA).