it's virtual money.. it started off as some dude who wanted to make his own monetary system not based on banks... he started some big code and set a number limit on how much money could ever be created by his system.. if you crack the codes, he pays you x amount of bc's for your work. they call this mining for some odd reason.. when bc's first came out, you'd get a nice pay out of bc's for your work, but at the time they didn't have much value to them... now they're up to $30 a bc if what da'ath said is true, which i'm not doubting him.. i know only like 3 months ago, they were only $13 per bc, so they have really gone up in the past few months..
once all the bitcoins are mined, there will never be anymore of it created, unlike the $ in which they print more at will, fucking up the economy and the value of it in the process..
bc's are now being accepted at lots of places online instead of real money or even paypal and credit cards, not just the silk road..
check out the story of the dude who created it if you're interested, it's pretty interesting..