Ever wondered how Gmail does its thing? I mean it's the fastest web-based email that I know of. Well behind every product of Google is an approach called AJAX. Ajax translates to Asynchronous Javascript And XML. It's not a technology but is simply a coming together of several technologies. These technologies are and not limited:
  + XHTML and CSS - standard based presentation
  + Document Object Model -  dynamic display and interaction
  + XML and XSLT -  data interchange and manipulation
  + XMLHttpRequest -asynchronous data retrieval
  + Javascript - binding technology of the above.

It can also be thought of an approach - a way of thinking about the architecture of web applications using certain technologies. It's a sort of a paradigm shift.

For more Information about AJAX you could visit http://www.adaptivepath.com/publications/essays/archives/000385.php, an essay written by James Garett of Adaptive Path (the one who coined the word AJAX) describes in a nutshell what AJAX is and what'll do for you.

Ever used AJAX? Comment on it here, all comments and suggestions are welcome. Flame on!