Ajax - Brief Discussion?

[FrOzeN]

Could anyone provide a good definition of what AJAX exactly is, and does?

I'm trying to grasp more concepts of web design so I can make my pages more interactive.

Also, when you click "Preview" here it generates the preview without reloading the page. Is that done via AJAX?

Currently, the only way I know of updating the page without reloading it is via hidden iFrames, a quick example I made:
[ [url=http://www.clananthrax.net/test/example.php]Page[/url] ] - [ [url=http://www.clananthrax.net/test/example.phps]Source[/url] ]

Note: I only used php in the example so I didn't have to make multiple pages, it isn't necessary for the concept.

[ober]

AJAX is used to make calls to the server and update portions of the page on the client side without refreshing the entire page.

If you want more info, check out www.ajaxfreaks.com (one of our other sites).  There are some tutorials over there and some other help that you might find useful.

And I don't really use the Preview function here, but there is AJAX hidden all over the SMF interface.