An excessively large, let alone loud exaust on a car, mainly on the so called "rice burners", "ricers" etc. Apparently they figure that the louder one's car sounds, the faster. Also needs a minimum diameter of 6'' or 7''. In the end, as a result, these cars sound like beavers passing gas in the mud.
When I was walking down the street the other day, I heard this ungodly noise, so I turned around to see this "souped" up Import car coming by, and of course, fitted with an extra loud fart cannon. I could only laugh... I always say "Flat 6 internal combustion, accept no substitute. Only by Porsche."