Twitter is a social networking and microblogging service that enables its users to send and read messages known as tweets. Tweets are text-based posts of up to 140 characters displayed on the author's profile page and delivered to the author's subscribers who are known as followers. Senders can restrict delivery to those in their circle of friends or, by default, allow open access. Since late 2009, users can follow lists of authors instead of following individual authors.[4][5] All users can send and receive tweets via the Twitter website, Short Message Service (SMS), or external applications (notably including those developed for smartphones). While the service itself costs nothing to use, accessing it through SMS may incur phone service provider fees. The website currently has more than 100 million active users worldwide.[6]

Since its creation in 2006 by Jack Dorsey, Twitter has gained notability and popularity worldwide. It is sometimes described as "SMS of the Internet."[7] The use of Twitter's application programming interface for sending and receiving text messages by other applications often eclipses direct use of Twitter.

What we have to do is deliver to people the best and freshest most relevant information possible. We think of Twitter as it's not a social network, but it's an information network. It tells people what they care about as it is happening in the world.