What is the difference between AC and DC electricity?

Direct current (DC) flows in one constant direction, like the current from a battery. Alternating current (AC) periodically reverses direction, switching back and forth many times per second (60 times per second, or 60 Hz, in North American household power). AC is used for power distribution because it can be easily transformed to different voltages for efficient long-distance transmission. DC is common in batteries and electronic devices. Many devices use a power adapter to convert AC from the wall into the DC the electronics need. Knowing the AC/DC distinction is fundamental.