“Social media” is a broad term, but it has come to be fairly well understood by example now. Facebook, Twitter, LinkedIn, YouTube, Tumblr, SnapChat, InstaGram, Pinterest, Google+ … These are the most common ones at the moment. What they are from a business perspective are tools for interactive marketing. That is, you are not just posting a billboard for people to look at, but posting something that they can interact with. That interaction requires some commitment on your part as well, so be prepared before you start.