In its form, money can be a special commodity, a security, a sign of value, various goods or values, account entries. The main functions of money are distinguished: a medium of exchange, a unit of account, a store of value, and sometimes a standard of deferred payment. Any object or verifiable record that performs these functions can be considered money.
Money is historically an emerging market phenomenon that creates commodity money, but almost all modern monetary systems are based on fiat money. Paper money, like any check or IOU, has no use value as a physical commodity. It derives its value by being declared legal tender by the government; that is, it must be accepted as a form of payment within the country for "all debts, public and private".