mason’s mitre
When stone moldings, cills, string-courses, etc., are continued around an angle, the point where they change direction must not coincide with the joint because an acutely angled piece of stone is subject to damage and easily snapped off. The joint, therefore, is formed at right angles to the naked of the wall at a distance from the angle, the change of direction of the molding effected by cutting it to shape. See reprise. (Curl & Wilson, 2016)