Alternating current

Alternating current (AC), is an electric current which periodically reverses direction, whereas direct current (DC, also dc) flows only in one direction. Alternating current is the form in which electric power is delivered to businesses and residences, and it is the form of electric energy that consumers typically use when they plug kitchen appliances, televisions and electric lamps into a wall socket. A common source of DC power is a battery cell in a flashlight. The abbreviations AC and DC are often used to mean simply alternating and direct, as when they modify current or voltage.
Ver en Wikipedia.org