AJAX is an acronym for "asynchronous JavaScript and XML".  It is one of the latest fads in "state of the art" high performance websites.  It basically means using javascript programming running on the users computer to process inputs from the user.  The result is generally displayed without having to reload the page.  If information is required from the server, it is requested using an XML exchange with the server, and again, the results are displayed on the page without reloading the entire page.

AJAX is one of the more difficult technologies to implement on a website, but it may be the best way to go for some high-performance features.  The best known example of AJAX in action is Google's gadgets - many of these small applications make extensive use of AJAX.

One simple example on our own site here is our page for: Estimating the Cost of your Website
This page uses AJAX to compute an estimated cost for your website by keeping a running total as you add up the features you require for your website.  Notice that the page never reloads, but the latest total is always displayed and updated every time you make another entry.

Another example of the use of AJAX is shown on our weather station: AhwatukeeWeather.com
The home page of this site uses AJAX to refresh the weather station report and the webcam image every minute, without the need for the user to reload the entire page. The user can view this page for hours and the 2 images remain current.