Brake booster definition
A mechanical device which attaches to the brake system to multiply the force the driver applies with his foot (or hand as in the case of a motorcycle ). The device uses air, vacuum, or hydraulic fluid to accomplish this purpose. Sometimes called "power assisted brakes," "vacuum assisted brakes," "hydraulically assisted brakes," or just "power brakes." In most cars, the boost comes from engine intake vacuum. In motorcycles it comes from hydraulic fluid.