Final answer:
A shortage occurs when prices are held below the market price, causing the quantity demanded to exceed the quantity supplied. This is typically a result of price ceilings.
Step-by-step explanation:
A shortage occurs when prices are held below the market price, causing the quantity demanded to exceed the quantity supplied. This is typically a result of price ceilings, which are enacted to keep prices low for consumers. When the market price is not allowed to rise to the equilibrium level, quantity demanded exceeds quantity supplied, and a shortage occurs.