volts (electrical pressure) of alternating current is referred to as VAC (AC). In the United States, a wall socket typically provides 110 to 120 volts of power.
The quoted AC voltage is an average of the real voltage, therefore 120 volts AC actually oscillates between zero and 170 volts in one direction and between zero and 170 volts in the other.
This particular average, which represents the equivalent power of 120 volts of direct current (DC), was determined using the RMS method, which stands for root-mean-square. In the United States, an alternating current cycle happens 60 times each second. In most of Asia and Europe, alternating current cycles 50 times each second.