Income effect

Income effect is a change in price affects the buying power of income, with a higher price meaning that the buying power of income has been reduced, so that there is usually (with normal goods) an incentive to buy less of both goods, and a lower price meaning that the buying power of income has been increased, so that there is usually an incentive to buy more of both goods; always happens simultaneously with a substitution effect.

Definition

According to Principles of Economics by Timothy Taylor (3rd edition),

Income effect. A change in price affects the buying power of income, with a higher price meaning that the buying power of income has been reduced, so that there is usually (with normal goods) an incentive to buy less of both goods, and a lower price meaning that the buying power of income has been increased, so that there is usually an incentive to buy more of both goods; always happens simultaneously with a substitution effect.

According to Macroeconomics by Mankiw (7th edition),

Income effect. The change in consumption of a good resulting from a movement to a higher or lower indifference curve, holding the relative price constant. (Cf. substitution effect.)