What ia a PWM?

A PWM stands for a Pulse Width Modulator, Its a swich that turn on/off.

The speed of the PWM depend on many factors, most dc motor controller run at a frequency of about 15khz or 15,000 times per second.

A basic AC frequency is 60hz or 60 times per second.

So the PWM is a pulse that turns the power on/off.