A cat-back exhaust system is an aftermarket upgrade for a vehicle's exhaust system that replaces the exhaust components located after the catalytic converter. This typically includes the muffler, resonator, and piping. The purpose of a cat-back exhaust system is to improve exhaust flow and enhance the sound of the exhaust note. By reducing exhaust restrictions and back pressure, a cat-back exhaust can improve engine performance and increase horsepower and torque. The name "cat-back" refers to the fact that the catalytic converter, which is responsible for reducing harmful emissions, is not replaced or modified as part of this system.