Electronics Engineering Question:

Pulse width modulation is a modulation technique in which the width of the pulse is varied in accordance with the message signal. Pulse width Modulation is abbreviated as PWM.
PWM can be used to reduce the total amount of power delivered to a load without losses normally incurred when a power source is limited by resistive means. This is because the average power delivered is proportional to the modulation duty cycle. With a sufficiently high modulation rate, passive electronic filters can be used to smooth the pulse train and recover an average analog waveform.

PWM is used in sound synthesis circuits.