From ml2sig
According to the Twitter FAQ, "Twitter is a service for friends, family, and co–workers to communicate and stay connected through the exchange of quick, frequent answers to one simple question: What are you doing? Bloggers can use it as a mini-blogging tool. Developers can use the API to make Twitter tools of their own."
People can update their Twitter feeds via text message or on the web, and can receive twitter updates in a variety of different forms, including text message and RSS feed.
Getting Started
This video is a great introduction: Twitter in Plain English
