A demand curve is a graphical representation of the relationship between the price of a good or service and the quantity demanded for a given period of time. It is a line graph that shows how many units of a good or service will be purchased at each possible price. The price is plotted on the vertical (Y) axis while the quantity is plotted on the horizontal (X) axis. Demand curves are used to determine the relationship between price and quantity, and follow the law of demand, which states that the quantity demanded will decrease as the price increases.

A demand curve can be a useful tool for businesses because it can show them the prices at which consumers start buying less or more. It can point out prices at which a company can maintain consumer demand and support reasonable profits. The demand curve is based on the demand schedule, which is a table that shows the quantity demanded at each price. Once plotted, the demand curve slopes downward, from left to right. As prices increase, consumers demand less of a good or service.

In summary, a demand curve is a graphical representation of the relationship between the price of a good or service and the quantity demanded for a given period of time. It is a line graph that shows how many units of a good or service will be purchased at each possible price. Demand curves are used to determine the relationship between price and quantity, and follow the law of demand, which states that the quantity demanded will decrease as the price increases.