Twitter is a social network that allows the user to publish individual texts with a maximum length of 140 characters. The main themes of each message posted on Twitter are user-defined and may be reported via a hashtag, which is a word that is preceded by a "pound sign", which facilitates the collection and retrieval of similar content posts. First created in 2006 in San Francisco, Twitter today is an essential information tool and monitors the dissemination of news on the net. In 2006, Jack Dorsey, one of the founders of Odeo, a company that specialized in podcasts, decided to create a social network that was focused on communication through SMS. With his partners, Biz Stone, Evan Williams, and Noah Glass, he investigated the creation of a micro blogging service that would be based on a limited number of characters. The result was Twitter, a social network that features a Blue Bird as its logo.
In 2007, Twitter became an independent company based in San Francisco. The number of micro-blog posts written by users, which are called Tweets, literally meaning "chirping", ranged in 2007 from 20,000 to 60,000 per day, and increased to 65 million in 2010 and 500 million in 2013. Every day Twitter users publish more than 500 million messages: 60% of which are sent from mobile devices. In November 2013, Twitter was publicly traded on the New York Stock Exchange. Despite its growing success, Twitter, does not have an advertising business model, and ended 2013 with a net loss of $645 million. On January 22, 2010, astronaut, Timothy Creamer, sent the first tweet from space. Since that day, NASA astronauts regularly send updates using the account @NASA_Astronauts.