1. A vehicle containing one or more hot pieces of female ass. You want to hit all of them.
2. A man's hog. This is a euphemistic definition deriving from the fact that after hammering on a woman's kitty, a man's penis can have a fragrance reminiscent of dead tuna fish.
Dave: "Hey, look at that carload full of poontang!"
Chester: "Yeah, that's a real tuna boat!"