Twitter is an online news and social networking service where users post and interact with messages, known as "tweets. " These messages were originally restricted to 140 characters, but on November 7,... wikipedia.org
Definition #2 for "twitter"
Twitter is a social networking and microblogging website where people can share short messages up to 140 characters long called tweets via a web interface, SMS texting or mobile apps. People can subscribe to other users by following them individually or by following a Twitter list, which are curated by a user and contain a group of different authors. These messages can also be retweeted, which shares the tweet with another person?s followers, similar to the Tumblr reblog function.