From the site:
"Second Life is a 3-D virtual world entirely created by its Residents. Since opening to the public in 2003, it has grown explosively and today is inhabited by millions of Residents from around the globe.
* From the moment you enter the World you'll discover a vast digital continent, teeming with people, entertainment, experiences and opportunity. Once you've explored a bit, perhaps you'll find a perfect parcel of land to build your house or business.
* You'll also be surrounded by the Creations of your fellow Residents. Because Residents retain the rights to their digital creations, they can buy, sell and trade with other Residents.
* The Marketplace currently supports millions of US dollars in monthly transactions. This commerce is handled with the in-world unit-of-trade, the Linden dollar, which can be converted to US dollars at several thriving online Linden Dollar exchanges."