Danielin odgovor je sasvim u redu, a od mene samo mali dodatak.
RO-RO je skraćenica od roll on/roll off, to su specijalni brodovi koji se koriste za teretni prevoz vozila (u tome je razlika u odnosu na feribote).
Encyclopaedia Britannica precizira:
When the cargo has wheels--e.g., automobiles, trucks, and railway cars--the most satisfactory cargo handling method is simply to roll it on and off. Vehicle ferries have been familiar in many waters for many centuries, and the growth since about 1960 of an extensive international trade in motor vehicles has led to an extension of the ferry principle into roll-on/roll-off ships, which carry automobiles strictly as cargo yet load and unload them by driving them on their own wheels.