Alternating Current

electric current which periodically reverses direction

An alternating current (AC) is an electrical current whose magnitude and direction vary cyclically, as opposed to direct current, whose direction remains constant. The usual waveform of an AC power circuit is a sine wave, as this results in the most efficient transmission of energy. However in certain applications different waveforms are used, such as triangular or square waves.
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Current /cur·rent/ 1. anything that flows. 2. electric c. action current the current generated in the cell membrane of a nerve or muscle by the [more]Alternating current - Community and Resources

Noun
1. an electric current that reverses direction sinusoidally; "In the US most household current is AC at 60 cycles per second"
(synonym) AC
(antonym) direct current, DC
(hypernym) electricity, electrical energy

electrical current that reverses direction at regular intervals, for example 60 Hertz in the U.S.