Oscar Brown said..
Web browsers are the most popular user interface for new applications. Still, they’ve traditionally suffered from a significant limitation: Each new request from a user requires a round-trip to the Web server, commonly resulting in loading a new page. A more intelligent—and faster—approach would be to access data in the background whenever possible, then update only those parts of the page that change. Users would see much more responsive applications, since they would spend less time waiting for new pages to be loaded.
This is exactly what’s done by the AJAX approach to building Web applications. Rather than load a new page for each user request, the browser asynchronously requests data in advance. The code that makes this request is typically written in JavaScript, and the data is often (although not always) formatted in XML. These three characteristics—Asynchronous JavaScript and XML—are the source of name AJAX.