g Money is best defined as whatever serves society in three functions: medium of exchange, store of value, and unit of account. whatever the government allows money to be. paper bills and coins. Barter is best defined as a situation where two individuals each want some or service that the other can provide. literally trading one good for another without using money. an informal market such as a flea market. A double coincidence of wants is a situation in which money is used to facilitate economic transactions. a situation where two individuals each want some or service that the other can provide. literally trading one good for another without using money.