Concept of Utility:
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In the ordinary language, `utility` means `usefulness`.

In Economics, utility is defined as the power of a commodity or a service to satisfy a human want.

Utility is a subjective or psychological concept. The same commodity or service gives different utilities to different people. For a vegetarian, mutton has no utility. Warm clothes have little utility for the people in hot countries. So utility depends on the consumer and his need for the commodity.

Marginal Utility:
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Marginal Utility is the addition made to the total utility by consuming one more unit of a commodity. It is additional utility derived from an extra unit of commodity consumed.

Total Utility:
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Total Utility refers to the sum of marginal utilities of all units of a commodity which are consumed. For example, if a consumer consumes ten biscuits, then the total utility is the sum of satisfaction (marginal utility) of consuming all the ten biscuits.