Money is not a commodity medium of exchange, but a social technology composed of three fundamental elements. The first is an abstract unit of value in which money is denominated. The second is a system of accounts, which keeps track of the individuals’ or the institutions’ credit or debt balances as they engage in trade with one another. The third is the possibility that the original creditor in a relationship can transfer their debtor’s obligation to a third party in settlement of some unrelated debt.
Felix Martin, Money: The Unauthorized Biography—From Coinage to Cryptocurrencies (New York: Alfred A. Knopf, 2013)