According to Rheingold, "A virtual community is a group of people who may or may not meet one another face to face, and who exchange words and ideas through the mediation of computer bulletin boards and networks. Like an other community, it is also a collection of people who adhere to certain (loose) social contract, and who share certain (eclectic) interests --Howard Rheingold, 'Virtual Communities,' 1987" (p. 162).
According to Rheingold (2012), Barry Wellman describes community as"networks of interpersonal ties that provide sociability, support, information, as sense of belonging and social identity" (p. 163). Somethings computer-mediated relationships can be called virtual communities. For Rheingold, "the difference between an online social network and a community has to do with the quality, continuity, and degree of commitment in the relationships between members" (p. 163).
Virtual worlds
According to Rainie and Wellman (2012), virtual worlds different from augmented reality and mirror worlds because they are online "places" where all content is graphically simulated, rather than projecting information onto the real world" (p. 284).
References:
Rainie, H. & Wellman, B. (2012). Networked: The New Social Operating System. Cambridge: MIT.
Rheingold, H. (2012). Net Smart : How to Thrive Online. Cambridge, MA, USA: MIT Press.