A coupe or sedan trunk that is absurdly large on the inside and deceptively small looking on the outside. A regular car trunk might be able to store a dead body or two, but a mafia trunk must be capable of storing at least 5 dead bodies.
Examples include the trunks on the Nissan Altima, Chevy Impala, and Mazda 3.
You want a Mazda 3? How are you going to get all of your stuff to college in one trip?
No worries, Mom; it's got a mafia trunk.
You stole a Mazda 3? How are we going to get Joey Malone's crew to the lake before sunrise?
No worries, Boss; it's got a mafia trunk.