"In economics, currency refers to a generally accepted medium of exchange. These are usually the coins and banknotes of a particular government, which comprise the physical aspects of a nation's money supply. The other part of a nation's money supply consists of bank deposits (sometimes called deposit money), ownership of which can be transferred by means of cheques, debit cards, or other forms of money transfer. Deposit money and currency are money in the sense that both are acceptable as a means of payment.
Money in the form of currency has predominated throughout most of history. Usually (gold or silver) coins of intrinsic value (commodity money) have been the norm. However, nearly all contemporary money systems are based on fiat money – modern currency has value only by government order (fiat). Usually, the government declares the fiat currency (typically notes and coins issued by the central bank) to be legal tender, making it unlawful to not accept the fiat currency as a means of repayment for all debts, public and private." MORE