The Bitcoin network is designed to mathematically generate no more than 21 million Bitcoins and the network is set up to regulate itself to deal with inflation. Bitcoins can be spent by initiating a transfer request from a Bitcoin address in the customer's wallet to a Bitcoin address in the vendor's wallet. As of this writing, one Bitcoin (also called a BTC) is worth $104 -- but just as with stocks, the value of Bitcoins can fluctuate quickly.
In the United States, Bitcoins are controversial because they can be used to anonymously transfer illicit funds or hide unreported income from the Internal Revenue Service (IRS). Bitcoin policy now requires transactions that involve traditional, government-backed currencies to be attached to an identity.