Twitter is a social networking and microblogging service. Users use any device with an internet connection and a web browser to send and to read messages, called "tweets". For years, tweets could be up to 140 characters long, then doubled in November 2017 to 280 characters. They appear on the user's profile page. Tweets can usually be read by anyone, but senders can also keep messages private. Private tweets only go to their list of friends. Users may subscribe to tweets from other people. This is called following, and subscribers are known as followers. As of late 2009, users can also follow lists of authors.
All users can send and receive tweets using the Twitter website. They can also use other applications that work with Twitter on smartphones. Twitter by Short Message Service (SMS) is available in certain countries. Using Twitter is free, but sending or getting tweets by SMS may cost money. The website is based in San Francisco, California. Twitter also has servers and offices in San Antonio, Texas and Boston, Massachusetts, and soon in Salt Lake City, Utah.
Twitter has become very popular worldwide since Jack Dorsey created it in 2006. It now has more than 126 million users. It is sometimes described as the "SMS of the Internet."
On April 25, 2022, the Twitter board of directors agreed to Elon Musk's USD $44 billion offer to buy the company. On October 27, 2022, Elon Musk took control of the company and fired CEO Parag Agarwal along with other top executives.