Hydraulic discs are a type of braking system commonly used in bicycles and vehicles. They consist of a disc rotor attached to the wheel and hydraulic calipers that squeeze the rotor to create friction, slowing down or stopping the vehicle. This system provides consistent braking power and better performance in various weather conditions compared to traditional rim brakes. The hydraulic mechanism allows for smoother and more responsive braking. When the brake lever is pulled, hydraulic fluid is pushed through the lines to the calipers, which then clamp down on the disc. This design reduces the effort needed to brake and enhances overall control and safety.