Google  

What is social media?

Social media is a way for people to bring their friends on to the internet, it's also more traditionally a way that people have been able to understand what's useful on the internet based on social interaction, what humans actually do. A good example would be Amazon, for years they've said people who have brought this item have also brought this item, that is someone saying this is probably a good recommendation for you. New sites as well do it really well, they'll have the most read article today or most commented article today, this will guide you to some of the more fresh content that they have on their site. It's become more mainstream recently with things like my space and face book where you actually log on and create a profile, and specifically call out your friends. Sites like twitter have made it easy to communicate on line without having to have a formal relationship.