Final answer:
Demand refers to how much of a product consumers are willing to buy at a certain price. Aggregate demand includes all components of demand and represents total spending on goods and services.
Step-by-step explanation:
Demand refers to how much (quantity) of a product or service is desired by buyers. The quantity demanded is the amount of a product people are willing to buy at a certain price; the relationship between price and quantity demanded is known as the demand relationship. Aggregate demand (AD) refers to the amount of total spending on domestic goods and services in an economy. It includes all four components of demand: consumption, investment, government spending, and net exports (exports minus imports).