1. A social networking website for people who need to stay on top of current events in real-time, which generally means reading some 12-year-old's commentary on an article that was posted on cnn.com several hours ago.
2. The 2000's equivalent of the AOL keyword... a medium by which businesses and news sources can publish small amounts of information to people who normally wouldn't care, but who will gobble the information up because the medium of transfer makes them feel like an "insider"
Person 1: Hey did you hear the news about Bono this morning?
Person 2 (frantically logging onto Twitter): I'm on it! Ah yes here's the story: "Man that Bono is some character, but I like his music from teh 80's #Bono RT RT"... I better re-tweet this quick. We twitterers count on each other to spread hot stories like this so we can stay ahead of the curve.