In economics, utility refers to the satisfaction or benefit that consumers derive from consuming a product or service.[1] Marginal utility on the other hand, describes the change in pleasure or satisfaction resulting from an increase or decrease in consumption of one unit of a good or service. Marginal utility can be positive, negative, or zero.[citation needed]

For example, when eating pizza, the second piece brings more satisfaction than the first, indicating positive marginal utility. However, after the third or fourth piece, the satisfaction level starts to decrease, indicating zero or negative marginal utility.[citation needed] Negative marginal utility implies that every additional unit consumed causes more harm than good, leading to a decrease in overall utility. In contrast, positive marginal utility indicated that every additional unit consumed increases overall utility.[2]

In the context of cardinal utility, economists postulate a law of diminishing marginal utility. This law states that the first unit of consumption of a good or service yields more satisfaction or utility than the subsequent units, and there is a continuing reduction in satisfaction or utility for greater amounts. As consumption increases, the additional satisfaction or utility gained from each additional unit consumed falls, a concept known as diminishing marginal utility. This idea is used by economics to determine the optimal quantity of a good or service that a consumer is willing to purchase.[3]
https://en.m.wikipedia.org/wiki/Marginal_utility