Web 2.0: What is Social Networking?

A social network service focuses on building online communities of people who share interests and/or activities, or who are interested in exploring the interests and activities of others. Most social network services are web based and provide a variety of ways for users to interact, such as e-mail and instant messaging services.

Social networking has encouraged new ways to communicate and share information. Social networking websites are being used regularly by millions of people.

From Wikipedia