AJAX = Asynchronous Javascript And Xml.  Microsoft has a project called Atlas which will deliver some solid AJAX stuff to VS2005 via an addon pack.

Things planned for Atlas include:

• Atlas client script framework
• ASP.Net Server controls for Atlas
• ASP.Net Web Services integration
• ASP.Net Building Blocks for Atlas
• Client Building Block services

If you missed the blog entry by Scott Guthrie about Atlas, and its something you are interested in - you should check out the Scotts blog entry!

UPDATE: Fixed typo.