This document discusses the concept of utility in economics. It defines utility as the want-satisfying power of a commodity or service. Utility is subjective and depends on the intensity of a person's wants. There are two approaches to measuring utility - the cardinal approach which measures utility numerically, and the ordinal approach which orders preferences. Total utility is the sum of utilities from consuming different units, while marginal utility is the change in total utility from an additional unit. The law of diminishing marginal utility states that the marginal utility of a good diminishes as more of it is consumed. There are some exceptions to this law such as rare goods. The law of diminishing marginal utility is significant as it forms the basis for other economic concepts.