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 July 2014, Twitter has more than 500 million users, out of which more than 271 million are active users.
Users can group posts together by topic or type by use of hashtags – words or phrases prefixed with a "#" sign. Similarly, the "@" sign followed by a username is used for mentioning or replying to other users. To repost a message from another Twitter user and share it with one's own followers, a user can click the retweet button within the Tweet. In late 2009, the "Twitter Lists" feature was added, making it possible for users to follow (as well as mention and reply to) ad hoc lists of authors instead of individual authors.
Tweets are publicly visible by default, but senders can restrict message delivery to just their followers. Users can tweet via the Twitter website, compatible external applications (such as for smartphones), or by Short Message Service (SMS) available in certain countries. Retweeting is when a tweet is forwarded via Twitter by users. Both tweets and retweets can be tracked to see which ones are most popular. While the service is free, accessing it through SMS may incur phone service provider fees. Users may subscribe to other users' tweets – this is known as "following" and subscribers are known as "followers" or "tweeps", a portmanteau of Twitter and peeps. Users can check the people who are unsubscribing them on Twitter ("unfollowing") via various services. In addition, users can block those who have followed them. Twitter allows users to update their profile via their mobile phone either by text messaging or by apps released for certain smartphones and tablets.
The company experienced rapid growth. It had 400,000 tweets posted per quarter in 2007. This grew to 100 million tweets posted per quarter in 2008. In February 2010, Twitter users were sending 50 million tweets per day. By March 2010, the company recorded over 70,000 registered applications. As of June 2010, about 65 million tweets were posted each day, equaling about 750 tweets sent each second, according to Twitter. As of March 2011, that was about 140 million tweets posted daily. As noted on Compete.com, Twitter moved up to the third-highest-ranking social networking site in January 2009 from its previous rank of twenty-second.