What is Marginal Utility?
Utility is the satisfaction after consuming a good.
Marginal utility is the added satisfaction that a consumer gets from having one more unit of a good or service. The concept of marginal utility is used by economists to determine how much of an item consumers are willing to purchase.
The Law of Diminishing Marginal Utility
As more of a good is consumed, eventually each additional unit of the good provides less additional utility--that is, marginal utility decreases. Each subsequent unit of a good is valued less than the previous one. The good becomes less scarce for the individual absolute satisfaction, Ceteris Paribus.​