What AJAX does, basically, is allow content on Web pages to update immediately when a user performs an action, unlike an HTTP request, during which users must wait for a whole new page to load.
Perhaps the best-known application to use AJAX is Google Maps. The interface allows the user to change views and manipulate the map in real time.
Some observers suggest that AJAX may be overhyped. Forrester's Root calls it "more like a different flavor of Java Applets than a complete Web revolution." Blogger Alex Bosworth thinks its power may lead to dangers for Web developers, as far as introducing UI and server load problems.
While you'll undoubtedly be hearing more about AJAX on SearchDomino.com in the months ahead, you can already read several stories to bring you up to speed. In fact, we've already had our first AJAX-related tip.