Definition of: Twitter A Web site and service that lets users send short text messages from their cellphones to a group of friends. Tweets are text-based posts of up to 140 bytes in length. Updates are displayed on the user's profile page and delivered to other users who have signed up to receive them. Senders can restrict delivery to those in their circle of friends (delivery to everyone being the default). Users can send and receive updates via the Twitter website, (receive only), or through applications such as Tweetie, Twitterrific, Twitterfon and Feedalizr.
Twitter is a social networking and micro-blogging service that enables its users to send and read other users' updates known as tweets
Twitter is a free service that lets you keep in touch with people through the exchange of quick, frequent answers to one simple question: What are you doing?