What is the term for the vertical wall of a ship?

The term for the vertical wall of a ship is "bulkhead." Bulkheads serve multiple purposes in a vessel, including providing structural support, dividing different areas of the ship into compartments (which can enhance safety by preventing water from flooding the entire vessel), and contributing to the overall stability of the ship.

In contrast to the bulkhead, the hull refers to the entire body of the ship that sits in the water, which includes the bottom, sides, and deck. The keel is the backbone of the ship running along the bottom, giving it structural strength and stability. Railings are the barriers typically found along the edges of decks to prevent people from falling overboard, but they do not serve the same structural functions as bulkheads. Thus, understanding the specific role and definition of a bulkhead highlights its importance in ship design and safety.