PWM - acronym definition request

[Michael Stegbauer]

PWM = Pulse Wave Modulation.

Typically a solenoid is used to bleed some pressure away from the
wastegate line allowing for more boost than the wastegate would
mechanically allow under whatever circumstances.

This solenoid only has two positions: open and close.
By opening and closing the solenoid very quickly with a given duty 
cycle, an ECU can simulate a valve that is X percent open.
It's a cheap man's stepper motor.

Mike