AJAX - Again, Just Another eXtension
Ajax is no big deal. Ajax just means that you can reload a little part of a web page instead of completely reloading the entire web page just to update that part.
Everybody's really excited because Microsoft and Google have been creating some high profile web pages that work this way. Actually, the idea isn't new. For a long time, scripts in web pages have loaded images and plugins from the server into parts of the pages. And when people were satisfied with simple rectangular areas to divide the parts of the page which would change independently, any data could be loaded on demand in "frames" and even inline frames, called "iframes". Even Google maps just uses an iframe, which has been around for ages.
There's a lot of hype going around about Ajax because it means people are finally starting to do some things the way they should have been done all along. But is it any more revolutionary, than, say, when those links started lighting up when you moved your mouse over them? I don't think so. Eventually Ajax will probably just be a little gimmick everybody and their brother will use in all their web pages- like those light-up links. It has little real impact on the character or functionality of the web.