An Alternating Current (AC) is an electric current that periodically reverses direction. The frequency of this reversal is measured in Hertz. There are broadly two categories, those AC signals used to carry power and those used to carry information. AC used for power transfer usually runs at nominally 50 Hz in Europe, Australia and other places, and 60 Hz in the Americas. It is normally sinusoidal. AC used to carry information can take a variety of waveforms, square, sinusoidal, ramp or some combination thereof. The frequency used can be anything from a few hertz up to several tens of gigahertz. Examples include audio, data, etc.