AJAX

Asynchronous JavaScript And XML. An acryonym containing another acronym (XML). It stands for the ability of web applications to retrieve content and communicate with a remote server without doing an additional full-page load. Portions of content can be loaded in the background, and messages can be sent to a remote server similar to a traditional networked application. Many internet web applications are written using AJAX, as browsers ubiquitously support the technology required to perform AJAX.

Oddly, AJAX functionality:

• Does not have to be asynchronous
• Does not have to use XML (often JSON and HTML are retrieved instead]]

AJAX on Wikipedia