What passes as Pulse Width Modulation in DC Motor Control?

Can anyone please tell me what passes as PWM in Motor Control?

Is it limited to supplying the motor with a square wave, where a set and
constant level of voltage is switched on or off to the motor?

Or can other waveforms consitutute PWM control of a dc motor? Such as where
voltage does not drop to zero, but has periodic peaks having square,
triangular, sawtooth or some other waveform?

Can PWM control consist of dc pulses that rise and fall in voltage in a
sinusoidal fashion?

At the moment I am believing that PWM is just on/off of a contant level of dc voltage. But wonder if that belief is correct or not. Thanks.
.

Relevant Pages

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