Alternating current (AC) and direct current (DC) are types of voltage that are used for transmitting electricity. DC is constant energy that moves in one direction, whereas AC changes and moves in a wave-like pattern.
Electricity arrives at consumer locations via AC, which, due to the shape of the current, can travel longer distances than DC. It powers lamps and appliances. Flashlights and other battery-powered devices use DC power. A laptop computer uses both: AC power is delivered from the wall outlet and transformed (in the black box that is part of the power cable) on its way to the machine, where it delivers DC to the computer battery.