Commodity money system
A commodity money system is a monetary system such as the gold standard in which a commodity such as gold is made the unit of value and physically used as money, any other money, such as paper notes, being theoretically convertible to it on demand. An historical alternative which was rejected in the Twentieth Century was bimetallism, also called the "double standard", under which both gold and silver were legal tender.
The alternative to a commodity money system is fiat money which is defined by a central bank and government law as legal tender even if it has no intrinsic value. Typically fiat money is paper currency or base metal coinage, but can also be simply data such as bank balances and records of credit or debit card purchases.
Today's global monetary system is essentially a fiat system because we can use paper bills or bank balances to buy goods. 
- Velde, Francois R., Following the Yellow Brick Road: How the United States Adopted the Gold Standard. Economic Perspectives, 4th Quarter, 2002. Available at SSRN: http://ssrn.com/abstract=377760 or doi:10.2139/ssrn.377760
- Historical documents, including discussions and debates regarding the use of various monetary standards
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