Technically, while they are both PWM, servos use a particular kind of PWM - called PPM, or "Pulse Position Modulation".
It's a form of PWM in which the length of the pulses determine the angle of the servo itself. Center being a 1.5 ms (millisecond) pulse, with each end-point extreme being represented by a 1 or 2 ms pulse - with all of the channels repeated within a 20 millisecond "window" of time (IIRC). For example, one servo:
...and multiple servos (or channels):
