Twitter is a free social networking and micro-blogging service where users post short messages (up to 140 characters) usually describing their current activities. The service was created by Jack Dorsey, Biz Stone, and Evan Williams, as an inside company system, and was launched for public use in August 2006.
Since 2006, the popularity of the service has rocketed, and now it's being used by over a million people, including celebrities, politicians and famous journalists. Twitter users can post messages, called 'tweets', and subscribe to each other's channels and become 'followers' to receive updates. The distribution of tweets can be restricted to one's circle of friends, or left in a default setting as visible to all users. Updates can be sent and received through the Twitter website, instant messaging, SMS, RSS, email or through an application such as Twitterrific or Facebook. The messages posted on Twitter range from simple notes about users' lives, to updates about coferences, political campaigns and events of world importance. Users' profiles contain basic information and have a simple form, and the service has a very consistant graphic design. There are hundreds of tools and applications that can be used with Twitter to make it more functionable, and easy to access from any place on Earth, and many clones, or services based on the same idea.