Currency is any document or thing which represents a monetary value, is payable to the bearer on demand, and represents legal tender. Banknotes and coins are typical forms of currency. It may be based on a valuable commodity, such as gold, or merely be supported by confidence in its value (fiat currency).
Currency must be distinguished from cash, which also includes demand notes (such as a check or other bill of exchange) for money on deposit. Currency by its definition must be payable to the bearer, not a beneficiary or payee. It also must be legal tender - acceptable without exception to pay a debt.