Thanks to saud264 from the forums for posting this in our BPN
ASP.NET AJAX is a free framework for quickly creating a new generation of more efficient, more interactive and highly-personalized Web experiences that work across all the most popular browsers. Many of the most popular ASP.NET component and solution vendors have also released new versions of their products with ASP.NET AJAX support.
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 requests a change. This is meant to increase the web page"s interactivity, speed, and usability.