What term describes all floors that are above the main deck on a ship?

The term that describes all floors that are above the main deck on a ship is "overhead." In naval terminology, any surface or area located above the main deck is referred to as overhead. This distinction is important as it helps crew members navigate and understand the structure and layout of the ship.

The primary deck serves as the base level from which other areas are measured, and the overhead provides a clear indication of the spaces that are located above this level, including various compartments, passageways, and operational areas. This terminology is particularly relevant for understanding the vertical layout and organization of shipboard spaces.

Other terms, like “deck,” may refer to various levels of a ship, but are not specifically indicative of areas above the main deck. Meanwhile, “underdeck” generally describes areas below the main deck, and “above deck” could be vague or context-dependent, making primarily "overhead" the correct and precise term to identify the floors above the main deck.