Twitter is an online social networking service that enables users to send and read short 140-character 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 more than 25 offices around the world.
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 more than 100 million users who in 2012 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." As of December 2014, Twitter has more than 500 million users, out of which more than 284 million are active users.
Twitter emphasized its news and information-network strategy in November 2009 by changing the question asked to users for status updates from "What are you doing?" to "What's happening?". On November 22, 2010, Biz Stone, a cofounder of the company, expressed for the first time the idea of a Twitter news network, a concept of a wire-like news service he has been working on for years.