Rice, generally referring to an Asian make of vehicle, Rocket generally referring to the speed or power of that particular vehicle. A true Rice Rocket means that the owner has tricked out his/her ride with actual engine/performance equipment to allow it to go faster. Often times, the owner will also do external/internal appearance mods to give the vehicle a racey look. Some people, however, forget to do engine/performance mods, and only do external appearance mods, meaning they don't have a a true Rice Rocket. They have a typical Asian vehicle that may or may not look fast, depending on the mods done to it. In recent times, "Rice Rocket" has been used to describe not only cars of Asian origin, but also some cars of European and North American descent that have been tricked out to go and look fast.
Hey, look at Tai Pai over there in his Rice Rocket...Man, the $12,000 he put into his Civic's engine mods, ground FX, rims and suspension really paid off. He killed that Mustang GT that cost $20,000. But look over there, Tai Pai's little brother Ling Lee tried racing the same Mustang GT. He got killed, because the Ground FX and Coffee-Can exhaust didn't do anything on that Corolla. Guess he doesn't have a true Rice Rocket!