Source: Wikipedia (http://en.wikipedia.org/wiki/Ajax_(programming) 4. Oktober 2007 / 3:45 MEZ

Ajax, or AJAX, is a web development technique used for creating interactive web applications. The intent is to make web pages feel more responsive by exchanging small amounts of data with the server behind the scenes, so that the entire web page does not have to be reloaded each time the user requests a change. This is intended to increase the web page's interactivity, speed, functionality, and usability.

...Continue on Wikipedia