Supply and Demand: The relationship between the quantity of a product or service available in the market (supply) and the desire for it by buyers (demand).
Opportunity Cost: The value of what is given up when making a choice. For example, if you choose to go to a party instead of studying for an exam, the opportunity cost is potentially getting a lower grade.
Utility: The satisfaction or usefulness that someone derives from consuming a good or service. It helps economists understand why people prefer certain choices over others.