Coin of account

A coin of account is a unit of money that does not exist as an actual coin (that is, a metal disk) but is used in figuring prices or other amounts of money. For example, the mill is a coin of account in the United States. It is equal to one-tenth of a penny, and so to one-thousandth of a dollar (= $0.001), whence the name, which means "thousandth," but there was never such a coin minteded, and it is used for figuring taxes, usually either property taxes or sales taxes.