(MOTOR) PHASE: A motor phase is a set of electrically excited stator poles, consisting of one or more pairs of oppositely polarized poles. The magnetic polarity of these poles is sequentially reversed when the number of phases are even integers, in which case the electrical angle between phases is 180 deg./number of phases. When the number of phases are odd integers, the polarity of the poles does not reverse and the electrical angle between phases is 360 deg./number of phases.
NOTE: A bifilar wound set of poles constitutes one motor phase, not two, since the flux reverses in the pole albeit the pole has two windings and the current in each is unidirectional. The number of phases is not dependent on the number of windings, but rather on the electrical angle between the poles.
What this means for the APS is that the most commonly used stepper motors are 2-phase, 4-winding motors.