What is social network? | Definition from TechTarget

A social network is a website that allows people with similar interests to come together and share information, photos and videos. 

People engaged in social networking may be doing so as a personal or a business endeavor. Those who engage on social network sites as a personal endeavor interact by using various forms of media to discuss their lives and interests. The most popular social networks for this type of familiar interaction include Facebook, Google+ and Twitter. Although these and other social networks may be used for business purposes — especially marketing — social networks exist specifically for enterprise social networking. Popular enterprise social network platforms include Socialcast and Yammer. Ideally, employees who are tasked with participating on social networks are provided with a social media policy so there is no ambiguity about what management considers to be acceptable use.