The volt-ampere, symbolVA, is the unit commonly used to express apparent power. At a terminal pair, RMS potential difference in volts multiplied by RMS current in amperes gives the numerical value in volt-amperes. The unit product has the same coherent SI dimensions as the watt:This unit identity does not make apparent power and active power the same quantity. The SI text explicitly warns that different physical quantities can share a unit and that the quantity must be specified.[ref]
The International System of Units (SI), ninth edition, SI Brochure. NIST SP330 parallel text, §2.3.4, coherent derived units and quantity identification
For an original example,250V RMS at8A RMS gives2000VA, or2kVA. If the absorbing load has power factor0.75, its active power is1500W. A1500W value cannot be inferred from the2kVA alone without the phase/waveform information summarized by that factor.
Hypothetical equipment can have separate apparent- and active-power limits. A1000VA/600W limit would permit a500W, factor0.5 load only at the apparent-power boundary, since it requires1000VA. A700W, factor-one load would require only700VA but exceed the separate600W limit. These examples interpret stated numerical constraints rather than specify an actual product's behavior.
For single-frequency sinusoids, the magnitude of complex electrical power is expressed in volt-amperes, while its real part is commonly expressed in watts and its imaginary part in reactive volt-amperes. Those names help keep the quantities distinct even though their base-unit dimensions agree.[ref]
AC Power Flow in Linear Networks by James L. Kirtley Jr.. Energy and Power, equations61–63; §7.1 RMS Amplitude
With distorted signals, retain the actual RMS-product definition of apparent power rather than assuming a single fundamental phasor accounts for all current. New to topics? Read the docs here!