In a recent thread, someone (who may, or may not, have been Robin2, not sure) said that controlling a servo was PWM. I personally never call it that.
In PWM we're concerned with the duty cycle, the on/off ratio, and the absolute on-time is not the point. Arduino offers PWM of two different frequencies: the practical result of using either is the same. So I get 1/2 speed with an analogWrite(pinX, 127) if I use a pin that gives 980 or 490Hz. Absolute on-time differs by a factor of 2 but the ratio is the same and so my motor runs at 50%.
With a servo otoh, we are concerned with the absolute width, and pulses of 1000 or 1500 or 2000us have totally different results. The on/off ratio is no longer the point, the absolute on-time is.
So, although servo control is clearly to do with Pulse Width, I don't think it's Pulse Width Modulation.