A "chock" is a __________.

The correct answer is that a "chock" is a casting fitted at the side of a weather deck, used as a fairlead. Chocks are typically installed at the points where mooring lines pass through, helping to guide the line and prevent it from chafing against the deck or other surfaces. These fittings ensure that lines are lead smoothly, helping to maintain the integrity of the mooring system and enhancing safety aboard.

While other options present different docking and securing practices, they do not accurately capture the primary function or definition of a chock in maritime terminology. For instance, being a deck fitting used to secure mooring lines speaks more to cleats or bollards, which serve different yet related purposes. Similarly, the mention of hygroscopic cargo relates to cargo handling practices rather than mooring equipment, while a smoke pipe for the galley stove pertains to ventilation systems on a vessel, entirely outside the context of securing or guiding lines. Therefore, the specific role of a chock as a fairlead makes it distinct and appropriate as the correct definition.