The term 'Maritime Upright' is a nautical term referring to the mainmast of a sailing vessel. The mainmast is the tallest mast on a ship and is used to support the sails. It is typically located near the center of the ship and is an important part of the rigging system. The term 'Maritime Upright' is used to describe the mainmast in its upright position, as opposed to when it is laid down or removed from the ship.