Equilibrium: The point at which quantity demanded and quantity supplied are equal.

Disequilibrium: Describes any price or quantity not at equilibrium; when quantity supplied is not equal to quantity demanded in a market.

Excess Demand: When quantity demanded is more than quantity supplied.

Excess Supply: When quantity supplied is more than quantity demanded.

Price Ceiling: A maximum price that can be legally charged for a good or service.

Price Floor: A minimum price for a good or service.

Price Control: A price ceiling on rent.

Minimum Wage: A minimum price that an employer can pay a worker for an hour of labor.

Surplus: Situation in which quantity supplied is greater than quantity demanded; also known as excess supply.

Shortage: Situation in which quantity demanded is greater than quantity supplied; also known as excess demand.

Search Costs: The financial and opportunity costs that consumer pay when searching for a good or service.

Supply Shock: A sudden shortage of a good.

Rationing: A system of allocating scarce goods and services using criteria other than price.

Black Market: A market in which goods are sold illegally.

Spillover Cost: Costs of production that affect people who have no control over how much of a good is produced.