What do 'walls' refer to in the context of a ship?

In the context of a ship, 'walls' refer specifically to bulkheads. Bulkheads are vertical partitions that divide the interior of a vessel into different compartments or sections. They serve several important functions, such as enhancing the structural integrity of the ship, providing stability, and improving safety by containing flooding in a specific area if a leak occurs.

Understanding the role of bulkheads is crucial for ship design and safety protocols, as they directly affect how a ship can withstand various stresses and emergencies at sea. The other choices, although parts of a ship's internal structure, do not accurately represent what is commonly referred to as 'walls.' Decks are horizontal surfaces, passageways are corridors for movement, and ceilings refer to the overhead structures, but none of these serve the specific function of 'walls' as bulkheads do.