Master cylinder in an automobile braking system is a hydraulic device in which cylinder and one or two pistons are arranged in such a manner that the mechanical force applied by the driver of a vehicle either by brake pedal (in cars) or by brake lever (in bikes) is converted into hydraulic pressure which in turn transferred to the brake calliper for braking.

In hydraulic braking system, master cylinder is a device that provides required amount of pressure or braking force to the final braking components after multiplication of the mechanical force applied by the driver through brake pedal or brake lever.