This is the 2012 LearnX Presentation that I did in Melbourne. Some of the slides may seem a bit odd out of context, but you'll get the gist of it if you're just patient. ;)
A virtual world is an online community that takes the form of a computer-based simulated environment through which users can interact with one another and use and create objects.(Bishop, J. (2009). Enhancing the understanding of genres of web-based communities: The role of the ecological cognition framework. International Journal of Web-Based Communities, 5(1), 4-17.)