This subject really needs more space than this forum provides. The US used a bi-metal system for many years, coins in both solid gold and silver. The gold coins were eliminated in 1933 under FDR. The silver was removed later. Today all US coins are worthless tokens. Paper currency used to be called either gold or silver certificates "redeemable to the bearer on demand" at any bank in gold or silver, the note merely being a receipt. Today paper currency (fiat) represents nothing but faith.