demand  The quantity of a good or service that consumers are both willing and able to buy at various prices.

law of demand  An economic law stating that as the price of a good or service increases, the quantity demanded decreases, and vice versa. Generally, consumers are happier to buy goods and services at lower prices than at higher prices.

substitute good   A product that satisfies the same basic want as another product. Substitute goods may be used in place of one another.

complementary good  A product that is used or consumed jointly with another product. Such a good usually has more value when paired with its complement than when used separately.

supply  The quantity of a good or service that producers are willing and able to offer for sale at various prices.

law of supply  An economic law stating that as the price of a good or service increases, the quantity supplied increases, and vice versa. Generally, producers are happier to offer goods and services at higher prices than at lower prices.

revenue  The amount of money a firm receives in the course of doing business. Revenue is calculated by multiplying the quantity sold by the price.

elasticity  A measure of the degree to which the quantity demanded or supplied of a good or service changes in response to a change in price.