Power in an electric circuit is the rate of energy consumption or production as currents flow through various parts comprising the circuit. In alternating current circuits, immediate power transferred through any phase varies periodically. Energy storage elements such as inductors and capacitors may result in periodic reversals of the direction of energy flow. The portion of power that, averaged over a complete cycle of the AC waveform, results in net transfer of energy in one direction is known as active power (sometimes also called real power). The portion of power due to stored energy, which returns to the source in each cycle, is known as reactive power.