Final answer:
Demand is the desire and ability to purchase a product or service based on needs, wants, and the ability to pay.
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.
Economists use the term demand to refer to the amount of some good or service consumers are willing and able to purchase at each price. Demand is fundamentally based on needs and wants-if you have no need or want for something, you won't buy it. Demand is also based on ability to pay.
In summary, demand is the desire and ability to purchase a product or service based on needs, wants, and the ability to pay.