Private Money Is Starting to Gain Traction

We all think we know what money is, but economists have many different definitions of money (e.g., M1, M2, M4, and others) — and the problem is getting worse. Is the U.S. paper dollar you have in your wallet money? How about a one-ounce gold $50 coin minted by the U.S. government, which has a current market value of roughly $1,200? Or digital bitcoins in your computer?