In economics, marginal utility describes the change in utility of one unit of a good or service. Marginal utility can be positive, negative, or zero. For example, when eating pizza, the second piece may bring 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 even negative marginal utility. 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.