Complements: are goods that are used in conjunction with other goods.

Cross-price elasticity of demand: the percentage change in demand divided by the percentage change in the price of another good.

Cross-price elasticity of supply: the percentage change in supply divided by the percentage change in the price of another good.

Elastic: the proportional change in quantity is greater than the proportional change in price (E > 1).

Elasticity: a measure of the responsiveness of one variable to another.

Excise tax: a tax that is levied on a specific good.

Income elasticity of demand: the percentage change in demand divided by the percentage change in income.

Inelastic: the proportional change in quantity is less than the proportional change in price (E < 1).

Inferior goods: goods whose consumption decreases when income increases. (Income elasticity is negative).

Jointly produced goods: goods in which the production of one good involved, as a byproduct, the production of another good.

Luxuries: normal goods that have an income elasticity greater than one.

Necessity: normal goods that have an income elasticity less than one.

Normal goods: goods whose consumption increases with an increase on income. (Income elasticity is positive).

Perfectly elastic curves: flat (horizontal) curves in which quantity changes enormously in response to a proportional change in price.

Perfectly inelastic curves: vertical curves in which quantity does not change at all in response to an enormous proportional change in price.

Price elasticity of demand: the proportional change in quantity demanded relative to a proportional change in price.

Price elasticity of supply: the proportional change in quantity supplied relative to a proportional change in price.

Price elasticity: a measure of the general responsiveness of quantity to change in price.

Quantity demanded: a specific amount that will be demanded per unit of time at a specific price.

Quantity supplied: a specific amount that will be supplied per unit of time at a specific price.

Substitutes: a good that can be used in place of another.

Unit elastic: the proportional change in quantity is equal to the proportional change in price (E = 1).