Twitter is a social media platform that allows users to post short messages, or tweets, of 140 characters or less. The document discusses key Twitter terminology like handles that begin with @, retweets indicated by RT, and favorites. It also explains how to get started using Twitter through a web browser, applications, or cellphone and provides tips for finding interesting people to follow based on their use of Twitter and interests. The document promotes having fun with Twitter and sharing content under a Creative Commons license.