The document discusses Twitter and microblogging. It defines Twitter as a free social media and microblogging platform where users share short bursts of information. Key aspects of Twitter discussed include following other users, hashtags to tag topics, trends showing popular topics, and the ability to see what your connections are doing in real-time. The document also notes some challenges of using Twitter for marketers in getting users to listen to brands among the large amount of information shared on the platform.