What deck is specifically referred to when discussing the uppermost structure on a vessel other than an aircraft carrier?

When discussing the uppermost structure on a vessel, the term that is specifically used is the main deck. The main deck serves as the primary working and living surface of the ship, providing the foundation for operations, equipment, and personnel. It is the highest complete deck on a ship and typically houses essential facilities and access to various parts of the vessel.

The weather deck refers to areas exposed to the elements, which could include several decks on a ship, not just the uppermost one. The flight deck is specific to aircraft carriers and is designated for launching and landing aircraft. The poop deck is a raised deck at the stern of the ship, often above the main deck, but it is not the primary uppermost structure of most vessels. Therefore, the main deck is the most accurate term to describe the overall top deck structure on a non-aircraft carrier ship.