"Second Life is a 3-D virtual social networking world entirely built and owned by its residents. Since opening to the public in 2003, it has grown explosively and today is inhabited by a total of 6,240,591 people from around the globe" (SecondLife.Com). Second Life allows users to create his or her own avatar, offering a lot of freedom in choosing one's own appearance. As a result, most Second Life users' avatars differ in looks from their real selves (for example, Jason, in Second Life, has green skin), and only very few create their Second Life avatars as a near exact representation of their real selves (like Henry Jenkins).
Second Life is unlike any other MMO because the goal or function of Second Life is entirely user-determined. As a result, the world of Second Life has been built from the bottom up to cater to almost anything a Second Life user could want, from creating original art and attending lectures to greed and lust. Some people and companies use Second Life as another means of economic success. Many large businesses (Reebok, Apple, and Nike, to name a few) have headquarters set up in Second Life that advertise their real life products.
http://www.secondlife.com/ Second Life Homepage