In the context of the Internet, the term "the social graph" usually refers to the connections between people who participate in a social networking service, such as Facebook, LiveJournal, LinkedIn or Myspace. Facebook founder Mark Zuckerberg has used the term, as well as the term social network, when discussing the relationships between users on Facebook, and how these relationships can make for what he calls a richer online experience. In mathematics, a graph is an abstract representation of relationships between things, and can be used to model various natural and man-made systems, such as power grids, economies, cells, and the World Wide Web. A social graph can be illustrated by drawing a diagram, where individuals are represented by nodes or dots, and their connections are represented by lines drawn between the nodes. The term can be used both to refer to the actual network of connections between individuals, and to a diagram that shows a representation of these relationships.
The terms social network and social graph are closely related. Usually, social networks refer to relationships in the real world, while social graphs describe relationships on the Internet, making them a representation of the social system online. However, the distinction is not a sharp one. Real world societies can be referred to as social graphs, where individuals are connected because they are related or because they know each other from various social settings, like work and school. Brad Fitzpatrick, a programmer and creator of LiveJournal, has described the social graph as a "global mapping of everybody and how they're connected."
Different social network services have their own social graphs that are usually completely separate from each other. In 2008, the Internet company Google Inc. started the Social Graph API, a project intended to make it possible for different websites, including social networking sites, to use publicly available information from the different online social graphs. In this context, the social graph includes not only relationships between individuals, but also connections to virtual objects like photos, pages, and events.
Proponents say that this use of social graphs will make it easier for people to interact with their entire social network online, regardless of what social networking service or website they are accessing. Critics call it a possible invasion of personal privacy. Some have also argued that each individual should have ownership and control over his part of the online social graph and the personal information it contains.