Twitter is a social networking service which enables users to send and read short messages called “tweets”. Users post these tweets on their timelines, which are made up of the tweets they follow and the ones they have themselves posted from. Users can also follow other people, who will then be notified when they post new content on Twitter. Tweets can be retweeted by others in order to increase their exposure; this is called “retweeting”. When someone retweets another person’s tweet it means that person has taken notice of it and wants everyone else who follows them to know about it too!