Twitter, Facebook, Myspace, MSN, ICQ, and lots of other bits of computer software have been called social networks. But why networks?
Yes I know they all run on computer networks but there's more to it than that. After all we talk about our network of friends and associates. Maybe network doesn't imply a computer network.
Turns out that there is a whole area of math that deals with the interconnections between things. You have friends and each of them has more friends. You are connected to your friends and they are each connected to all their friends. This branch of math is called network theory. Network theory helps explain things like six degrees of Kevin Bacon.
By the way... the 6 degrees of Kevin Bacon game works because Kevin Bacon has enough connections to other people in Hollywood to make it relatively easy to track back to him. He isn't the most central person in Hollywood. Central means the person who has the shortest path to everyone else. So an obscure actor who appeared in a single movie would not be central. An actor with lots of roles, lots of co-stars, and a long career would be much more central. According to the Oracle of Bacon (which sadly doesn't actually talk about the food bacon) the most central person in the IMDB database is Dennis Hopper. Karen Black is the leading woman on their list of The Center of the Hollywood Universe.
I stumbled across a good attempt to give an overview of network theory on a site called Measuring Measures called Learning Network Theory. If you want to explore the math behind social networking sites and 6 degrees of whomever it's a good place to start.