In 3-Axis satellite control movement around the X-Axis is called Roll.  Errors in this Axis will shift the pointing of the communications transmit pattern of the satellite in what appears to be a north/south movement on the earth.  Through the normal progression of an orbit Roll will translate to Yaw in a quarter of the orbit.  Both errors can be managed by active control and typically Roll control is chosen to be controlled if only one of the two Axis is to be controlled.  The diagram and animation show a visual representation of this movement.