Second Life is a privately owned, partly subscription-based 3-D virtual world, made publicly available in 2003 by San Francisco-based Linden Lab, and founded by former RealNetworks CTO Philip Rosedale. Users can visit this virtual world almost as if it were a real place. They explore, meet new people, participate in individual and group activities, and, if they decide to visit often, they learn new skills and mature socially (in the sense of learning the culture of the virtual world). Though sometimes referred to as a game, Second Life does not have points, scores, winners and losers, levels, an end-strategy, or most of the other characteristics of a game.
The Second Life “world” is simulated by a large array of servers, known collectively as “the grid,” that are owned and maintained by Linden Lab. A Second Life client program provides its users (often referred to as Residents) with tools to view and modify the SL world and participate in its virtual economy. The economy operates as a real free market. Residents buy and sell to one another, and the virtual currency is exchangeable for US$.
As of December 2006, ten to twenty thousand users are in SL at any one time. At 8:05:45 AM PDT, October 18 2006, the number of registered accounts in Second Life reached one million. Eight weeks later, on December 14 2006, this number doubled to two million, and that rapid growth continues. However, there is a difference between registered accounts and unique, returning users. Many accounts are created by users who log in once or a few times and never return, and some regular users have multiple active accounts. One analysis of the economy of Second Life suggests that the number of unique, regular users is around 100,000
Source:Wikipedia