DC vs. AC Current
Direct Current (DC): Electrons flow in one direction only. Produced by batteries. Constant voltage. Used in most portable electronics.
Alternating Current (AC): Electrons flow back and forth, reversing direction periodically. Produced by generators and the power grid. Standard frequency in North America = 60 Hz (60 complete cycles per second). Preferred for long-distance power transmission because transformers can easily step voltage up or down.