Final answer:
The term that describes the desirability of an object or service based on its relative worth is 'value'. A valued item must have scarcity and utility, the latter being the personal satisfaction derived from it. Economists also recognize the law of diminishing marginal utility, where additional satisfaction decreases as more of the same good is consumed.
Step-by-step explanation:
The term that best describes the relative worth of an object or service that makes it desirable is known as value. In economics, for something to have value, it needs to possess two main qualities: scarcity and utility. Utility reflects the usefulness or satisfaction derived from a good or service. When making a purchase, consumers seek items that provide the greatest utility, thereby optimizing their level of satisfaction or happiness from their choices. The worth of an item is often expressed in monetary terms but also accounts for personal satisfaction.
Additionally, it's important to understand the concept of the law of diminishing marginal utility. This law states that as a consumer enjoys more of a good, the additional satisfaction from consuming each successive unit decreases. For example, the first slice of pizza might bring immense satisfaction, while the sixth slice may not bring as much pleasure. This decrease in marginal utility is a common economic observation.