- amplitude modulation. information transmitted on a radio wave by varying the amplitude of the carrier. see FM.
- the time between 12 midnight and 12 noon. see PM. Civilized people tend to not use this system, but just tell the proper time. Ironically this system was taken over by the US army, probably to disgust the lefties in mainland Europe, or for its lack of confusing qualities, or because Americans are unable to master the frigging 24-hour clock.