This is a kind of money due to the government decree (or saying that is will be used as money).

Fiat Money

Explanation:

if the currency is without an intrinsic value (value because of the nature of tangible material used as money for e. g. govt issued banknotes) and become money because of government's decision it is called Fiat Money, it is opposite of commodity money (money created from precious metals like gold and silver) and representative money (money that represents something of value, but has little value of its own like paper money). Fiat money holds its value either because of regulation or agreement of parties engaging in its exchange.