What is the difference between pitch, roll, and yaw?

When some bearings of a translation stage are supporting more of the load than other bearings, there is an uneven loading on the stage. These offset forces are referred to as pitch, roll, and yaw. Pitch has its axis of rotation perpendicular and in the same plane as the direction of travel. Roll has the axis of rotation parallel to the direction of travel. Yaw has rotation perpendicular to the plane of travel. See the accompanying illustration below: