This is a way for example to renew a part of a web page without having to reload all the contents. For example you have a page for football match and you want to update the score along with the game, so you'd rather use ajax and update only the area where the score is than refreshing the whole page several times per minute. In fact what happens is that a JavaScript piece of code connects to the web server, retrieves the information needed, in this case the score, and displays it a predefined area on the already loaded in user's browser page.