Comet - the next stage of AJAX!

Comet is a software concept that enables web servers to send data to the client program (normally a web browser) without having any need for the client to request it. It allows creation of event-driven web applications which are hosted in the browser.

A style of data transmission that is neither traditional nor Ajax

Reference :
http://www.irishdev.com/NewsArticle.aspx?id=2166
http://en.wikipedia.org/wiki/Comet_(programming)