it's on online virtual world where you create a character and do stuff. like a huge 3d chatroom but you can create your own content with 3d modelling and C/Java style scripting. you can buy/sell land, etc. you can covert real money to/from in game currency, there are people with businesses in game that end up turning real life profits.
people make all sorts of things from mini arcade style games to strip clubs to nascar style racing simulations in the game.
it's been getting more press lately, lots of people are starting to take it seriously. intel occasionally gives press releases inside of second life, i heard the swedish government opened up an office there, etc.
you can play it for free or pay $10 which nets you the privelage of owning property and gives you a weekly allowance of ingame cash.
lots of people think it'll be the new wave of the future or something, a world where people can come together and chat or do whatever. think there's any potential for some erisian evangelism or whatever you want to call it?