Ajax
Asynchronous Javascript and XML is a relatively new technique for creating fast and dynamic web pages.
AJAX allows web pages to be updated asynchronously by exchanging small amounts of data with the server behind the scenes. This means that it is possible to update parts of a web page, without reloading the whole page. Classic web pages, (those that do not use AJAX) must reload the entire page if the any of the content should change. Ajax works essentially by wrapping the XMLHttpRequest method of the window object, checking the readystate and the status properties of this method, and targeting an element(s) in the document to receive the output response from the server.
Examples of applications using AJAX: Google Maps, Gmail, Youtube, and Facebook tabs.