What is Social Media?

The best way to define social media is to break it down. Media is an instrument on communication, like a newspaper or a radio, so social media would be a social instrument of communication.
In Web 2.0 terms, this would be a website that doesn't just give you information, but interacts with you while giving you that information. This interaction can be as simple as asking for your comments or letting you vote on an article, or it can be as complex as Flixster recommending movies to you based on the ratings of other people with similar interests.
Think of regular media as a one-way street where you can read a newspaper or listen to a report on television, but you have very limited ability to give your thoughts on the matter.
Social media, on the other hand, is a two-way street that gives you the ability to communicate too.