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