Definition: Complementary goods are two or more goods typically consumed or used together, such that a change in the price or availability of one good affects the demand for the other good.
Example: As we can see from the graph below; when the price of an iPhone decreases, the demand for iPhone cases increases. This is because the demand for iPhones increases as more consumers are buying it at the lower prices. In turn, those same consumers are demanding iPhone cases – which translates into high sales.
