The way we communicate, especially online, is changing. Now the biggest source of information are people rather than dedicated 'deities' on a particular subject like it use to be. Another thing that is totally unprecedented is the speed at which information travels. If anything happens in Syria, we all know about it out there in North America in a matter of seconds. In fact, we can probably see it through live feed or whatnot.
When you think of Social Media, you think of either Facebook or Twitter. Facebook is basically what started it all. Although there Phone Number List were lots of other similar services like MySpace (remember that one), Friendster and more, Facebook kept it simple and with some new innovative features, it caught on quickly. Once the college crowd took over it (The young professionals), it was over. Facebook is the biggest social network in the world.
Some say that Twitter is an offshoot of Facebook's status update feature. Facebook is used for communication with friends and customers while Twitter is a more 'instant' version of that. Needless to say, both should be part of your marketing arsenal.