Two or more. products are said to be complementary in demand when an increase in the price of one is generally associated with a decrease in demand for the other. Examples are bread and butter, cars and petrol, cigarettes and cigarette lighters. The complementarity stems from the nature of consumer tastes, which results in some products being habitually consumed together, or from some technical relationship which makes one necessary if the other is to be enjoyed. It follows that complementarity need not exist for all time - tastes may change or technology may alter. Goods having such complementarity are called complementary goods.
|Reference: The Penguin Dictionary of Economics, 3rd edt.|