Online social networking
An online social network is an internet-based services which allows people to create accounts and to use these accounts to build an online social identity, to communicate electronically with others, and to follow and respond to the electronic communications of others.
Examples of popular online social networking services are Facebook, MySpace, Twitter, Identi.ca and Moodle, but there are also many others: List of social networking websites. A wiki can also, arguably, be thought of as a social network.