Moving electrons constitute current. When the electrons move in single direction, it is known as Direct current (DC). When the electrons move back and forth, it is known as Alternating current (AC).
Voltage transferred from the power plants to out home is in the form of AC. A high voltage AC can be converted to low voltage AC and vice-versa using transformer.
DC is used for very small power requirement as such in cells of clocks, remotes etc. One single voltage can be supplied using DC. It cannot be increased or decreased.
