Ajax Overview

Ajax: Asynchronous JavaScript and XML

Question: What does the buzzword Ajax mean, anyway?

Answer: The term Ajax was coined by Jesse James Garrett, co-founder of Adaptive Path. The acronym Ajax (with only the first A usually capitalized) stands for Asynchronous JavaScript and XML; essentially, it serves as a marketing term denoting a set of technologies that together enable a new kind of Web applications.

An Ajax-based Web application, unlike a traditional Web site,

functions without reloading the Web page that hosts the application on the client computer;
extensively uses the Document Object Model (DOM) and JavaScript to implement the interactivity of the application;
relies on XMLHttpRequest calls (or a similar technique) to exchange information with the Web server;
performs the client-server data exchanges asynchronously, behind the scenes, while the user can continue interacting with the Web application in the Web browser.

Paul Graham gives the following characterization of Ajax-based applications in his essay Web 2.0:

Basically, what "Ajax" means is "JavaScript now works." And that in turn means that web-based applications can now be made to work much more like desktop ones. As you read this, a whole new generation of software is being written to take advantage of Ajax. There hasn't been such a wave of new applications since microcomputers first appeared.