A brake booster is a device in a vehicle's braking system that enhances the driver's braking power. It uses vacuum pressure, typically from the engine, to multiply the force applied to the brake pedal. This allows for easier and more effective braking, especially in larger vehicles that require more force to stop. When the driver presses the brake pedal, the brake booster helps to amplify this force before it reaches the brake system, which includes components like the brake calipers and brake pads. This results in a smoother and more responsive braking experience, improving overall vehicle safety.