Twitter is a social networking and blogging site created in 2006 that enables users to send and receive short messages referred to as "tweets". A tweet is a text-based message no longer than 140 characters long and us displayed on the author's profile page in twitter.  Each tweet is delivered to the people who subscribe to the author's page.  These subscribers are called "followers". 
 
Tweets can be went from the Twitter website or from a cellphone and the twitter service is free to use.  Currently there are over 100 million users of Twitter worldwide.
 
Twitter is a good way to keep up on the latest happenings of your friends or of celebrities and is very popular among the teenage set.  If you are a parent of a pre-teen or a teenager they are probably on Twitter.