Twitter started 2006 as a social networking/microblogging site developed by Jack Dorsey. In February 2009 it was ranked as the 3rd most popular social networking site on the internet. It is like Facebook, except stripped of everything except a profile picture and a status update. The updates, or "tweets," can be a max of 140 characters, and all the fellower Twitterers who watch your updates are called your followers.
I really can't stand this site because of just how much information people divulge on it. Everyone thinks they're a superstar, because anybody can set one of these accounts up. They write the most boring random updates and think that random people are spending their days watching all these updates. I remember I had to update my brother's Twitter account frame by frame at a bowling tournament in Vegas over the summer...and he only has 4 followers! As if they're sitting at their computers waiting for the next update to come in. And even the media is using this thing to let random people just post their opinions on worldwide news stories. CNN lets their fans tweet during the show, as do most of the ESPN shows now, and they barely filter what comes in! People just say anything, and so we learn very quickly how bored and uneducated society truly is.
Some useful sites for this subject:
A "How To" Guide to using Twitter
Twitter Mistakes to Avoid