In the study of microeconomics it can be helpful to quantify the utility value of goods. This is done using a theoretical unit of measurement called a util.
When the value of goods is quantified as utils, it makes it easier to model consumer behavior.
As the consumed quantity of a good increases, the value of each good tends to decrease. The value of one more of a good is called marginal utility. Utils can be used to quantify and model changes to marginal utility of a good at different consumption levels.