Twitter is an online social networking and microblogging service that enables users to send and read short 140-character text messages, called "tweets". Registered users can read and post tweets, but unregistered users can only read them. Users access Twitter through the website interface, SMS, or mobile device app.Twitter Inc. is based in San Francisco and has offices in New York City, Boston, San Antonio and Detroit.

Twitter was created in March 2006 by Jack Dorsey, Evan Williams, Biz Stone and Noah Glass and by July 2006, the site was launched. The service rapidly gained worldwide popularity, with 500 million registered users in 2012, who posted 340 million tweets per day. The service also handled 1.6 billion search queries per day. In 2013 Twitter was one of the ten most-visited websites, and has been described as "the SMS of the Internet."