Substitute Goods:Goods that can be used in place of one another, such as Coke and Pepsi, where an increase in the price of one good leads to an increase in the demand for the other.
Complementary Goods: Goods that are used together, such as printers and printer ink, where an increase in the price of one good leads to a decrease in the demand for the other.
Elasticity of Demand:The measure of the responsiveness of the quantity demanded of a good to a change in its own price.