Three-phase is a common method of electric power transmission.
It is a type of polyphase system used to power motors and many other devices.
Three phase has properties that make it very desirable in electric power systems.
Firstly the phase currents tend to cancel one another (summing to zero in the case of a linear balanced load).
This makes it possible to eliminate the neutral conductor on some lines.
Secondly power transfer into a linear balanced load is constant, which helps to reduce generator and motor vibrations.
Finally, three-phase systems can produce a magnetic field that rotates in a specified direction, which simplifies the design of electric motors.
Three is the lowest phase order to exhibit all of these properties.