This document discusses social networks and their usage. It defines a social network as a social structure made up of individuals and connections between them. It provides examples of popular social networks like Facebook, Twitter, and Google+ and describes how they allow users to connect online, share multimedia, create groups, exchange ideas and advertise. The document also notes some risks of using social networks like stalking and identity theft if private details are shared. It provides statistics on social network usage, finding that 47% of online adults and 73% of teens/young adults use social media, with many businesses and people spending significant time on platforms like Facebook.