Number of pulses per second or input frequency (1/s).
The speed of the ON-OFF signals applied to a stepper motor driver. The pulse rate, divided by the logical steps per revolution of the motor/driver combination, is the rotational speed in revolutions per second (RPS).
The frequency of the step pulses applied to a step motor driver. The pulse rate, multiplied by the resolution of the motor/driver combination (in steps per revolution), yields the rotational speed in revolutions per second.