Twitter is a social media platform that allows users to share messages called tweets that are limited to 140 characters. It was founded by Jack Dorsey, Evan Williams, Biz Stone, and Noah Glass and has grown to over 500 million users who use it to discover and share information in real-time on various topics and news. While initially used to connect people with shared interests, businesses now use it for marketing and promotion. During events like the Arab Spring, activists also used it to organize protests and share uncensored information.