Alternative term for Master Cylinder.
Master cylinders are used on braking systems to turn the mechanical power provided when you step on the brake pedal into the hydraulic power that is needed to apply the brakes and slow or stop the vehicle. The brake master cylinder is where the brake fluid reservoir is located on most vehicles. The reservoir stores the fluid until it is needed.
A cylinder containing a movable piston activated by pressure on the brake pedal. The piston produces hydraulic pressure that pushes fluid through the lines and wheel cylinders. This forces the brake lining or pad against the drum or disc to slow or stop the car.