"In an AC system, the charges of electricity move back and forth over a short distance. In other words, they sit inside the wires and vibrate. That's what AC or Alternating Current is all about. The electricity does not move forward at all (if it did, that would be a direct current or "DC.") Yet as the charges of electricity are wiggling back and forth, the electrical energy moves forward rapidly. Only the electricity "alternates." The electrical energy does not; the energy flows continuously forwards as waves. (If this is confusing, think of sound which moves through the air. Electricity is like the air which is vibrating. On the other hand, the electrical energy is like the sound waves which fly through the air.) Just as sound and air are two different things, electrical energy and electricity are two different things. "