1. Also called Plimsoll line. any of various lines marked on the sides of a cargo vessel to indicate the depth to which a vessel may be immersed under certain conditions. Cf. freeboard (def. 1a).
2. the line made by the surface of the water on the hull of a loaded ship.
Random House Unabridged Dictionary, Copyright © 1997, by Random House, Inc., on Infoplease.