Scarcity: limited availability of things that we desire (not to be confused with shortage). Utility

OPPORTUNITY COST: the highest valued benefits that must be given up when using a resource in a particular way. The highest valued alternative that is unavailable because a resource is used in some other way.

HUMAN RESOURCES: the quantity and quality of the labor force as a contributor to the production of goods and services.

CAPITAL GOODS: human-made, tangible resources used to produce goods. For example, factories, machines, and tools. (Not money or financial assets.)

EFFICIENCY: producing something at the lowest possible opportunity cost. Producing those goods that give us the most utility relative to what has to be given up.