ELASTICITY OF DEMAND. In economics, a term used to describe the degree of responsiveness of sales-volume to changes in the price of a given commodity. Marshall (Principles of Economics) puts it that "the elasticity of demand in a market is great or small according as the amount demanded increases much or little for a given fall in price, and diminishes much or little for a given rise in price." A commodity may at one and the same time, in the same mar ket, be in "elastic demand" by the poor and "inelastic demand" by the rich. Thus, if bananas fell in price to ten a penny, the demand of the well-to-do would not alter, because they would need no more than when bananas were a penny or twopence each, but the demand of the poor would be "elastic," and a greatly increased quantity would be sold. For a discussion of supply and demand, see EcoNoaiics.