Utility is a satisfaction that an individual derives from consuming or using a specific good or service. Total utility indicates the total amount of satisfaction or pleasure an individual derives from consuming some specific quantity of a good or service. Marginal utility refers to the additional satisfaction a consumer gets from an additional unit of a good or service she/he consumes during a given period of time.
The law of diminishing marginal utility states that as a consumer consumes more and more units of a specific good or service, the additional utility the consumer derives from the successive units keep on diminishing (declining) over time.
Diminishing marginal utility explains a lot about consumer behavior in the economy. Select a specific consumer behavior and construct a "mini case study" that highlights the workings of marginal utility and how it affects the consumption pattern.