Ship rig
A full rigged ship (a vessel with 3 or more masts, all square-rigged) is said to have a ship rig. Thus such a vessel is sometimes referred to as a ship, without regard to whether it fulfills other definitions of that word.
Related rigs are brig (2 masts), barquentine (square-rigged on only the fore mast), and barque (square-rigged on all but the mizzen mast).