Giffen good

In microeconomics and consumer theory, a Giffen good is a product that people consume more of as the price rises and vice versa, violating the law of demand.

For ordinary goods, as the price of the good rises, the substitution effect makes consumers purchase less of it, and more of substitute goods; the income effect can either reinforce or weaken this decline in demand, but for an ordinary good never outweighs it. By contrast, a Giffen good is so strongly an inferior good (in higher demand at lower incomes) that the contrary income effect more than offsets the substitution effect, and the net effect of the good's price rise is to increase demand for it. This phenomenon is known as the Giffen paradox.