complementary good

Material or good whose use is interrelated with the use of an associated or paired good such that a demand for one (tires, for example) generates demand for the other (gasoline, for example). If the price of one good falls and people buy more of it, they will usually buy more of the complementary good also whether or not its price also falls. Similarly, if the price of one good rises and reduces its demand, it may reduce the demand for the paired good as well. Also called complementary product.