Catback exhaust systems refer to any part of the exhaust system that's set-up behind the catalytic converter. Typically, this includes the pipe connecting the pipe from the catalytic converter to the muffler, the muffler, and the tailpipe or exhaust tips. When used in the context of aftermarket parts or performance upgrades, "cat-back" indicates which section of the parts' exhaust system was replaced. Cat-back systems are available as both single- and dual-exhausts.
Cat-back exhaust systems generally use larger diameter pipes than the stock system. If the system is engineered more for show than functionality, it may be tuned to enhance the lower sounds lacking from high RPM, low-displacement engines. Cat-back exhaust systems will include pipes that run from the catalytic converter to the muffler, the muffler itself, any pipes that may run from the muffler to the exhaust tips, and the exhaust tips themselves. However, some cat-back exhaust systems have a muffler delete, which means no muffler is included.