Rich Internet Application
The term AJAX stands for "Asynchronous Javascript and XML". AJAX allows web pages to be updated asynchronously by exchanging small amounts of data with the server behind the scenes. This means that it is possible to update parts of a web page, without reloading the whole page.
Technologies Used in AJAX

JavaScript: JavaScript function is called when an event in a page occurs.

DOM: Represents the structure of XML and HTML documents.

CSS: Allows for a clear separation of the presentation style from the content and may be changed programmatically by JavaScript.

XMLHttpRequest: JavaScript object that performs asynchrous interaction with the server.
Advantages of AJAX :
»    The smaller server resources footprint helps server scalability.

»    Reduce bandwidth.

»    Fast and flexible to more robust and manageable.

»    Client based to more server centric.

»    Library of rich components.

»    Interoperability with other solutions.

»    Speed and invisibility makes for a very slick user experience.

Ajax is about how to deliver information to end users in a way that is easier to understand, delivered faster and in a more intuitive way and for users to be able to communicate back to a host system more effectively.

Ajax techniques apply very well to most existing applications and can provide a very fast incremental improvement to an existing application. The frame work is equally valuable for upgrades to existing applications and for new applications.