AJAX

(Asynchronous JavaScript and XML). XJAX refers not to a scripting language (like JavaScript) but rather to a method for creating rich web interaction. JavaScript is one of those languages used to create this interaction, XML is the other one (though HTML can be used). The two work to manipulate the Document Object Model (DOM). but it is the asynchronous part that has ignited the use of AJAX.

With AJAX small trips are made to the server in the background, as the user interacts with the page without having to reload the entire page every time data is requested.

AJAX example; when you are using facebook and you are typing the name of a friend into a box sometimes it pops up below the box with a list of friends which match the first few letters which you have typed in. JavaScript is used to call the database where your list of friends are kept all in the background.