Ajax (sometimes called Asynchronous JavaScript and XML) is a way of programming for the Web that gets rid of the hourglass. Data, content, and design are merged together into a seamless whole. When your customer clicks on something on an Ajax driven application, there is very little lag time. The page simply displays what they're asking for. If you don't believe me, try out Google Maps for a few seconds. Scroll around and watch as the map updates almost before your eyes. There is very little lag and you don't have to wait for pages to refresh or reload.
Ajax is a way of developing Web applications that combines:

* XHTML and CSS standards based presentation
* Interaction with the page through the DOM
* Data interchange with XML and XSLT
* Asynchronous data retrieval with XMLHttpRequest
* JavaScript to tie it all together

In the traditional Web application, the interaction between the customer and the server goes like this:

1. Customer accesses Web application
2. Server processes request and sends data to the browser while the customer waits
3. Customer clicks on a link or interacts with the application
4. Server processes request and sends data back to the browser while the customer waits
5. etc....
Thanks.