Effective power
Effective power: In alternating-current
power transmission and distribution, the product of the rms
voltage and
amperage,
i.e., the
apparent power, multiplied by the
power factor,
i.e., the cosine of the
phase angle between the voltage and the current.
Note: Only effective power, i.e., the actual power delivered to or consumed by the load, is expressed in watts. Apparent power is properly expressed only in volt-amperes, never watts. Synonym true power.
Source: from Federal Standard 1037C