AJAX: an acronym that Jesse James Garret of AdaptivePath.com came up with in 2005. Just a few short years later, it seems like every site has a "taste" of AJAX in it. If you're totally new to AJAX, I'll just point out that, at its core, AJAX is nothing very scary or horrendous. AJAX isn't even a new technology or language.

Essentially, AJAX stands for: Asynchronous JavaScript and XML, and it is the technique of using JavaScript and XML to send and receive data between a web browser and a web server. The biggest advantage this technique has is that you can dynamically update a piece of content on your web page or web form with data from the server (preferably formatted in XML), without forcing the entire page to reload. The implementation of this technique has made it obvious to many web developers that they can start making advanced web applications (sometimes called RIAs—Rich Interface Applications) that work and feel more like software applications than web pages.

Keep in mind that the word AJAX is starting to have its own meaning (as you'll also note its occasional use here as well as all over the Web as a proper noun rather than an all-cap acronym). For example, a Microsoft web developer may use VBScript instead of JavaScript to serve up Microsoft Access database data that is transformed into JSON (not XML) using a .NET server-side script. Today, that guy's site would still be considered an AJAX site rather than an "AVAJ" site (yep, AJAX just sounds cooler).In fact, it's getting to the point where just about anything on a web site (that isn't in Flash) that slides, moves, fades, or pops up without rendering a new browser window is considered an "Ajaxy" site. In truth, a large portion of these sites don't truly qualify as using AJAX, they're just using straight-up JavaScripting. Generally, if you use cool JavaScripts in your Joomla! site, it will probably be considered Ajaxy, despite not being asynchronous or using any XML.

Want more info on this AJAX business? The w3schools site has an excellent introduction to AJAX, explaining it in straightforward simple terms. They even have a couple of great tutorials that are fun and easy to accomplish even if you only have a little HTML, JavaScript and server-side script (PHP or ASP) experience (no XML experience required): http://w3schools.com/ajax/.