Twitter is a social media platform that saw a huge increase in unique monthly visitors from 1.2 million in May 2008 to 18.2 million in May 2009. The document discusses how Twitter can be used as a conversation tool, for professional networking, sharing resources and breaking news, by government entities, and for searchable and shareable content. It also outlines how libraries can use Twitter to announce programs, send updates to followers' phones, and promote their services to gain followers on the platform.