What is Ajax?

1. Ajax the methodology - this is the concept, the approach: fetching small pieces of data from the server, without a whole page refresh.
2. Ajax the technology - the libraries and toolkits: JavaScript, Flash, XML, HTML, etc. whatever enables #1 above.
3. Ajax the implementation - it can be as boring (and useful!) as a "smart" HTML form that validates fields as you tab between them, or as sexy as Google Maps.

http://jszen.blogspot.com/2005/05/ajaxed-out.html