marginal utility

In economics, the marginal utility of a good or service is the gain from an increase, or loss from a decrease, in the consumption of that good or service. Economists sometimes speak of a law of diminishing marginal utility, meaning that the first unit of consumption of a good or service yields more utility than the second and subsequent units, with a continuing reduction for greater amounts. The marginal decision rule states that a good or service should be consumed at a quantity at which the marginal utility is equal to the marginal cost.