Social networking is the practice of expanding the number of one's business and/or social contacts by making connections through individuals, often through social media sites such as Facebook, Twitter, LinkedIn and Google+.
Based on the six degrees of separation concept (the idea that any two people on the planet could make contact through a chain of no more than five intermediaries), social networking establishes interconnected online communities (sometimes known as social graphs) that help people make contacts that would be good for them to know, but that they would be unlikely to have met otherwise.
Depending on the social media platform, members may be able to contact any other member. In other cases, members can contact anyone they have a connection to, and subsequently anyone that contact has a connection to, and so on. Some services require members to have a preexisting connection to contact other members.
While social networking has gone on almost as long as societies themselves have existed, the unparalleled potential of the Web to facilitate such connections has led to an exponential and ongoing expansion of that phenomenon. In addition to social media platforms, the capacity for social interaction and collaboration is increasingly built into business applications.
See a history of social media in less than 10 minutes: