A brig is a type of sailing vessel defined by its rig: two masts which are both square-rigged. Brigs originated in the second half of the 18th century and were a common type of smaller merchant vessel or warship from then until the latter part of the 19th century. In commercial use, they were gradually replaced by fore-and-aft rigged vessels such as schooners, as owners sought to reduce crew costs by having rigs that could be handled by fewer men. In Royal Navy use, brigs were retained for training use when the battle fleets consisted almost entirely of iron-hulled steamships.

The mast of a sailing vessel is a tall spar, or arrangement of spars, erected more or less vertically on the centre-line of a ship or boat. Its purposes include carrying sails, spars, and derricks, giving necessary height to a navigation light, look-out position, signal yard, control position, radio aerial or signal lamp. Large ships have several masts, with the size and configuration depending on the style of ship. Nearly all sailing masts are guyed.