VAC stands for volts of alternating current (electrical pressure) (AC). In the United States, normal wall socket voltage ranges from 110 to 120 volts.

The quoted AC voltage is an average of the real voltage, therefore 120 volts AC actually varies from 0 to 170 volts in one direction and from 0 to 170 volts in the other. This particular average is determined using the root-mean-square (RMS) approach and represents the equivalent power that 120 volts direct current (DC) provides. This cycle of alternating current happens 60 times per second in the United States. In Europe and the majority of Asia, alternating current cycles 50 times per second.