At the simplest level, it allows your web page to fetch portions of content/data from HTTP sources which may occur either as foreground or background processes.

More importantly, these requests can be triggered by DHTML events, such as onClick, onBlur, onFocus, onKeyPress, onMouseOver etc. The request usually returns XML data, but can in fact return anything your server can serve up.

Using JScript to fetch the data, you can then chop the data (if necessary) and set the value of elements within the page - either changing values of input items or re-writing parts of the page. You can also add and remove elements from the page, pop-up IFRAME helpers etc.

For some examples of Ajax at work:
   Xbase++ specific:
      www.shorttermcover.com/ajax.html (Phil Ide)
      ajax.eliasweb.nl/ (Sander Elias)

   Google
      Google Suggest
      Google Maps (UK)
      Google Maps (USA)

The link to the left will give you the complete project for building the Xbase++ demo that can be found at www.shorttermcover.com/ajax.html.