market share.The percentage of the market for a product that a firm supplies, usu. calculated by dividing the firm’s output by the total market output. • In antitrust law, market share is used to measure a firm’s market power, and if the share is high enough — generally 70% or more — then the firm may be guilty of monopolization. See MONOPOLIZATION. Cf. MARKET POWER. [Cases: Monopolies 12(1.3). C.J.S. Monopolies §§ 28–37, 52, 64–66.]

[Blacks Law 8th]