Mark Zuckerburg's concept "Social Graph"

The social graph is where you make connections between people, this is how facebook derived. The social graph draws an edge between people, places, and things and how the interact online. This concept is the foundation for other social networks as well, such as Twitter and Pinterest. Twitter allows followers to find people with  similar interests and topics to dicuss; whereas, Pinterest is a virtual pinboard allows you to pin and share things you find on the web.