Square rig is a generic type of sail and rigging arrangement in which the primary driving sails are carried on horizontal spars which are perpendicular, or , to the keel of the vessel and to the masts. These spars are called yards and their tips, beyond the last stay, are called the yardarms. A ship mainly so rigged is called a square-rigger.

Square rig is a generic type of sail and rigging arrangement in which the primary driving sails are carried on horizontal spars which are perpendicular, or , to the keel of the vessel and to the masts. These spars are called yards and their tips, beyond the last stay, are called the yardarms. A ship mainly so rigged is called a square-rigger.