A "cat-back system" refers to an aftermarket exhaust system that replaces the components from the catalytic converter to the rear of the vehicle. This includes the exhaust pipes, muffler, and tailpipe. The primary purpose of a cat-back system is to improve exhaust flow, which can enhance engine performance and increase horsepower. These systems are popular among car enthusiasts because they can also change the sound of the vehicle, often providing a deeper and more aggressive tone. Installing a cat-back system is generally straightforward and can be done with basic tools, making it an accessible upgrade for many car owners.