A term that describes the relationship between multiple time-varying waveforms which have a constant frequency but differ in their position relative to time. It is also used to refer to the number of sinusoidal voltages that make up the power delivery to a device. Most common are three-phase and single-phase. Single-phase consists of 2 conductors between which a sinusoidal voltage is present. Three-phase is a set of 3 or 4 conductors. In the case of 3 conductors, a sinusoidal voltage of a constant magnitude and frequency but differing relationship with respect to time exists between any 2 conductors. In a 4 wire system, the same voltage as in the 3 wire case exists between any of the three “hot” conductors and in addition, between any of the three “hot” conductors and fourth neutral conductor there exists a voltage that is smaller by a factor of the square root of three than the voltage between any of the “hot” conductors. An example of this is a 208/120 three-phase system. 208 volts exists between any of the three “hot” conductors and 120 volts exists between any of the “hot” conductors and the neutral conductor.