alternating current 
(abbreviation AC or ac)
noun
An electric current that reverses its direction many times a second at regular intervals, typically used in power supplies. Compare with direct current.LED lights require a transformer to turn alternating current to direct current....
- The company built a new mill and contracted with the Telluride Power and Transmission Company at Ames to supply electricity as an alternating current to both the mine and mill.
- In any case Edison's technique was limited by his insistence on using direct current, rather than the standard alternating current that soon took its place when the advantages were recognized.