Pump-handle is a movement of ribs that results in change in anteroposterior diameter of the thorax.
Definition
One of the most important functions of ribs and diaphragm, is the change in volume of thorax that helps inspiration and expiration. In general, the ribs move around two axes. The anterior end of the rib is lower than the posterior end, therefore, during elevation of the rib, the anterior end also moves forwards. Movement at costovertebral joints 2 to 6 about a side-to-side axis results in raising and lowering the sternal end of the rib, the "pump-handle" movement.This occurs mostly in the vertebrosternal ribs. In elevation, this increases the anteroposterior diameter of the thorax.
References
Pump handle movement Wikipedia(Text) CC BY-SA