Twitter is a social media platform that allows users to post short messages called tweets that are limited to 140 characters. Users can follow other users and see their tweets in their timeline. Tweets can be public or only visible to approved followers. Twitter began in 2006 and has grown significantly, with some describing it as the "SMS of the Internet." It allows for communication through features like replies, retweets, and hashtags that group tweets by topic. While initially considered a social network, Twitter's founder describes it as an "information network" that shares what people care about as events unfold in the world.