What exactly is a Catback. I haven't had much experience with them, so any explanations would be nice.

 

a catback is an exhaust... it's called a cat back because it goes from the Cat (catalytic converter) back... the cat is on the downpipe, and the downpipe connects to the catback, which is the muffler and the long pipe attached to it

 

From what i understand if you just get a muffler it changes the sound, if you get a catback (catalytic converter and a different muffler) it also increase performance. Because its less restriction and also means you may or may not pass emission laws depending on what you get.