This document defines and discusses virtual communities. It begins by defining a virtual community as a group of people who share common interests or ideas online. It then outlines different types of virtual communities like message boards, online chat rooms, and social networks. The document also discusses the advantages of virtual communities like socializing, working collaboratively, and having topic-based conversations. However, it notes potential disadvantages like less social interaction offline, cyberbullying, and reliability/identity issues with some information shared online.