Quarterdeck in the context of "USS Missouri (BB-63)"

The forecastle (/ˈfoʊksəl/ FOHK-səl; contracted as fo'c'sle or fo'c's'le) is the upper deck of a sailing ship forward of the foremast, or, historically, the forward part of a ship with the sailors' living quarters. Related to its latter meaning is the phrase "before the mast" which denotes anything related to ordinary sailors, as opposed to a ship's officers.

A spar is a pole of wood, metal or lightweight materials such as carbon fibre used in the rigging of a sailing vessel to carry or support its sail. These include yards, booms, and masts, which serve both to deploy sail and resist compressive and bending forces, as well as the bowsprit and spinnaker pole.

In larger vessels during the age of sail, spare spars could be roped together to provide a temporary surface known as a "spar deck". These served as jury-rigged repairs for permanent decks, or as an additional platform under which to shelter goods or crew. The term was also informally applied to areas of the forecastle or quarterdeck where spare spars were stored by laying them flat against the existing decking. In the modern era the term has been used to describe the uppermost deck on flush decked vessels.

Nuestra Señora de la Santísima Trinidad, nicknamed La Real, was a ship of the line of the Spanish Navy which was the largest warship in the world when launched. She originally mounted 112 guns, which was increased between 1795 and 1796 to 130 guns by closing in the spar deck between the quarterdeck and forecastle. In 1802 Santísima Trinidad was further upgraded to 140 guns, including four guns on the poop deck, effectively creating a continuous fourth gundeck, although the extra guns added were relatively small. She was the most heavily armed ship in the world when rebuilt, and bore the most guns of any ship of the line outfitted in the Age of Sail. Santísima Trinidad was captured by the Royal Navy on 21 October 1805 at the Battle of Trafalgar but was scuttled the next day.

Quartermaster is a military term, the meaning of which depends on the country and service. In land armies, a quartermaster is an officer or enlisted soldier who supervises logistics and requisitions, manages stores or barracks, and distributes supplies and provisions. In many navies, a quartermaster is a seaman or petty officer with responsibility for navigation and operation of the helm of a ship.

The term appears to derive from the title of a German royal official, the Quartiermeister. This term meant "master of quarters" (where "quarters" refers to lodging or accommodation). Alternatively, it could have been derived from "master of the quarterdeck" where the helmsman and captain controlled the ship. The term's first use in English was as a naval term, which entered English in the 15th century via the equivalent French and Dutch naval titles quartier-maître and kwartier-meester, respectively. The term began to refer to army officers in English around 1600.

In naval architecture, a poop deck is a deck that forms the roof of a cabin built in the rear, or "aft", part of the superstructure of a ship.

The name originates from the French word for stern, poupe, from Latin puppis. Thus the poop deck is technically a stern deck, which in sailing ships was usually elevated as the roof of the stern or "after" cabin, also known as the "poop cabin" (or simply the poop). On sailing ships, the helmsman would steer the craft from the quarterdeck, immediately in front of the poop deck. At the stern, the poop deck provides an elevated position ideal for observation. While the main purpose of the poop is adding buoyancy to the aft, on a sailing ship the cabin was also used as an accommodation for the shipmaster and officers. On modern, motorized warships, the ship functions which were once carried out on the poop deck have been moved to the bridge, usually located in a superstructure.