Pulse width modulation (PWM) is a type of digital signal that can be used to control the input voltage with digital position feedback signals, through a series of on-off pulses.  Pulse-Width Modulation is commonly used for speed control of a motor.  The wider the pulses the higher the average input voltage and the narrower the pulses, the lower the input voltage.
On actuators with an internal PCB, PWM is usually not allowed as it will damage the components on the board.