artice from wikipedia.com
Micro-blogging is a form of blogging that allows users to write brief text updates (usually less than 200 characters) and publish them, either to be viewed by anyone or by a restricted group which can be chosen by the user. These messages can be submitted by a variety of means, including text messaging, instant messaging, email, MP3 or the web.
The most popular service is called Twitter, which was launched in July 2006 and won the Web Award in the blog category at the 2007 South by Southwest Conference in Austin, Texas. The main competitor to Twitter has been Jaiku.
Recently, however, many new services, with the same feature of micro-blogging are being born. Digg founder Kevin Rose, together with three other developers recently launched a service called Pownce, which integrates micro-blogging with file-sharing and event invitations.
The popular social networking websites Facebook and MySpace also have a micro-blogging feature, called “status update”.
Web 2.0: Who, What, Why, How 