The Free On-line Dictionary of Computing (18 March 2015):
(Or "vertical refresh rate", "vertical scan rate")
The maximum number of frames that can be displayed on a
monitor in a second, expressed in Hertz.
The scan rate is controlled by the vertical sync signal
generated by the video controller, ordering the monitor to
position the electron gun at the upper left corner of the
raster, ready to paint another frame. It is limited by the
monitor's maximum horizontal scan rate and the resolution,
since higher resolution means more scan lines. Increasing
the refresh rate decreases flickering, reducing eye strain,
but few people notice any change above 60-72 Hz.