the principle that suggests the consumer derives less benefit or satisfaction from each additional unit of a product or service consumed or used; e.g., the consumer gets less extra benefit (i.e., marginal utility) from buying and eating each additional Snickers chocolate bar, or from each additional hot dog, pair of sunglasses, or radio. See marginal utility and law of diminishing returns. Note: popular usage in marketing is for the law of diminishing marginal utility and the law of diminishing returns to be used interchangeably.