Twitter is a public instant messaging service that allows users to post short messages called tweets. It has over 4 million users who post over 1 million tweets per day. Twitter can be used by businesses to get feedback, monitor conversations, and connect with customers and industry influencers. The document provides tips for businesses starting on Twitter, such as filling out a profile, following others, posting regularly, and engaging in conversations. It also discusses tools for managing Twitter accounts and potential legal issues.