Pulse Width Modulation. A method of controlling power by rapidly switching on and off. The ratio of on time (the pulse width) to off time determines output power. IE, starting with 12V, a PWM value of 50% provides an effective output of 6V, 75% 9V, etc. Used in switch-mode power supplies and sine wave dimmers (typical frequencies 40-400 kHz, and quite often for LED control in a color mixing fixture (typical frequencies around 1 kHz). Also used by Variable Frequency Drives and sine wave inverters to create a sine wave from a DC bus.