"Historically, there have been three categories of money: commodity, credit, and fiat. Commodity money consists of some durable material of intrinsic value, typically gold or silver coin, which has some value other than as a medium of exchange. Gold and silver have industrial uses as well as an aesthetic value as jewelry. Credit money refers to the liability of some individual or firm, usually a checkable bank deposit. Fiat money is a tax credit not backed by any tangible asset."This is a curious explanation of money because virtually no one considers or talks of credit as money or thinks of fiat money as a tax credit.
Source: Soft Currency Economics