AJAX isn't so much a single technology as it is a set of technologies that are now all part of most contemporary browsers. Because of this factor, it's sometimes difficult to explain what precisely AJAX is, especially the degree to which XML or JavaScript predominates.

Ever since the term AJAX was coined, the concept has spread like wildfire in developer communities. Lots of applications have been developed using AJAX. In fact, a lot of applications were developed using AJAX long before AJAX came into existence. In this section, we will go over some AJAX application examples to give the reader some sense of what AJAX is capable of and what applications have been built using it.

AJAX is a viable way to develop richer, more interactive Web applications. These kinds of applications are typically referred to as 'Rich Internet Applications' (RIAs). RIA is a term that describes the next-generation Web applications that combine the performance and functionality of desktop software with the universal deployment advantages of the Web.

Given the challenges associated with AJAX, it is particularly important to architect an AJAX application properly. Otherwise the result can be either lackluster performance or a code maintenance nightmare, or both.

AJAX has raised the awareness of the potential of Web applications. It has also deepened and broadened the use of JavaScript and DHTML in application development. There are significant benefits to AJAX, but there are also significant challenges.

AJAX changes the role of Web pages from being merely HTML documents into 'applications' that contain both HTML markup and code. And it changes the role of the 'server' from merely serving HTML pages to serving data too. In classic Web applications, Web servers serve HTML Web pages. Some of the pages are static; others are generated dynamically by server-side logic.

'Ajax, shorthand for Asynchronous JavaScript and XML, is a web development technique for creating interactive web applications. The intent is to make web pages feel more responsive by exchanging small amounts of data with the server behind the scenes, so that the entire web page does not have to be reloaded each time the user makes a change. This is meant to increase the web page's interactivity, speed, and usability.'