Twitter is based around the idea of allowing users to quickly post short messages called Tweets. It is a microblogging service. In 140 characters or less Twitter allows you to tell people what you are up to. To post and update you can use a desktop computer, instant messaging or a mobile phone.

If you know other Twitter users then you can “follow” their profile and read their Tweets and see what they are talking about. They can do the same by following your Tweets and you can respond to their Tweets.

http://www.twitter.com