Challenged with trying to describe Twitter to your friends?

According to the official Twitter FAQ, "Twitter is a community of friends and strangers from around the world sending updates about moments in their lives. Friends near or far can use Twitter to remain somewhat close while far away. Curious people can make friends. Bloggers can use it as a mini-blogging tool. Developers can use the API to make Twitter tools of their own. Possibilities are endless!"

You may have other ideas. "What is Twitter?," here are more Twitteresque descriptions.

Note: As you come across descriptions on the Web, please link to them here.

Complete this sentence: Twitter is...

Positive

• burst-messaging tool, credited to Robin Good
• group instant messaging, credited to Robyn Tippins
• instant access presence service, with potential for emergency warning systems, credited to Mark H Jones
• microblogging, credited to Nivi
• microblogging, una mezcla de blogging con red social y mensajería instantánea, credited to Jose Luis Orihuela
• mobile blogging, credited to Paul F. Roberts
• nano-blogging, credited to Carol Stimmel
• notification system, credited to Dave Winer
• round-the-clock updates, credited to BRAD STONE and MATT RICHTEL, New York Times article, April 30, 2007
• telling the world I exist, credited to damselseo
• a rushing river of brevities, credited to vaspers aka steven e. streight
• what makes us interesting, credited to ryryryry
• real-time expanding communal consciousness , credited to brent of brentjones.org