Boom

In maritime terminology, on a sailboat, a boom is a long spar (a pole) which runs along the foot of a fore and aft rigged sail. The boom’s main purpose is to make it easier to control the shape and angle of the sail and to ensure the foot is flatter when the sail angle is away from the centerline of the boat. The boom is tethered by a wire rope or tackle from aloft to its upper end, while its lower end is usually hinged and connected to the mast.