What is the lowest deck on a ship called?

The lowest deck on a ship is called the orlop deck (pronouned "or·lop"). It lies above the space at the bottom of the hull. The term is most often used for a ship that has four or more decks.

The word "orlop" was first used between 1375 and 1425. It derives from the late Middle English word "overloppe," meaning a covering, and the Middle Dutch word "overlopen," meaning run over.

The orlop typically lies below the water line and is the storage location for the ship's cables.

The term "orlop" is most commonly used to describe the bottom deck of a wooden sailing ship.