- The structure of the ship that lies above the weather decks (AKA the superstructure).
- The parts of the vessel above the waterline when fully laden.
Given the two different definitions, the meaning pretty much depends on who you’re talking to. I’ve always heard it in reference to the superstructure of a vessel.
Crowell, J. (2003, October 31). Naval Terminology, Jargon and Slang FAQ Part 2 – N through Z. Hazegray.org. http://www.hazegray.org/faq/slang2.htm.
Dictionary.com. (2020). Upper works. In Dictionary.com. https://www.dictionary.com/browse/upper-works.