Definition: a social graph is a diagram that illustrates interconnections among people, groups and organizations in a social network. Somewhat confusingly, the term is also sometimes used to refer to the social network itself, rather than a diagram of the network. Individuals and organizations, called actors, are nodes on the graph. Interdependencies, called ties, can be multiple and diverse, including such characteristics or concepts as age, gender, race, genealogy, chain of command, ideas, financial transactions, trade relationships, political affiliations, club memberships, occupation, education and economic status.
Services such as Facebook facilitate the exchange of information, news, photographs, literary works, music, art, software, opinions or even money among users. In this environment, the social graph or for a particular user consists of the set of nodes and ties connected, directly or indirectly, to that actor.
We invite you to watch this presentation from CommonCraft: Social Networking in Plain English.