For ac power as well as the watt (W) for real (or active) power electrical engineers use the volt-amp (VA) for apparent power and volt-amp-reactive (VAR).for reactive power.
For a purely resistive circuit real power and apparant power are the same and reactive power is zero.
For a circuit which has both resistance and reactance there will be a phase difference $\phi$ between the applied voltage and the current.
In such a circuit if you measured the rms value of applied voltage $V$ and the rms value of the current $I$ and multiplied the two quantities together you would get the apparent power $VI$ measured in $VA$.
Real power is a measure of the power supplied to the circuit by the power supply which does not come back to the power supply.
This power ends up as heat in the resistive parts of a circuit or used by motors to do work.
Real power $=VI \cos \phi$ where $\cos \phi$ is called the power factor of the circuit and this quantity is measured in watts.
If a circuit is purely inductive or purely capacitive then the phase angle between current and voltage is $\frac \pi 2$, $\cos \theta = 0$ and the real power is zero.
However that is not to say that there is no current flowing in the circuit.
During a cycle reactive components are supplied electrical power during one half of a cycle and then return the electrical power during the other half of the cycle.
The net electrical power dissipated by a reactive component is zero.
The amount of power going backwards and forwards between the circuit and the power supply is important and it is called the reactive power $(=VI \sin \phi)$ and has the unit VAR.
The relationship between the tree types of power is
$\rm power_{apparent}^2 = \rm power_{real}^2 + \rm power_{reactive}^2$
kWh is the kilowatt-hour and is a unit of energy.
It is the energy used by a device in one hour during which the power supplied to the device is one kilowatt.
$\rm 1\,kWh = 1000 \times 60 \times 60 = 3\,600\,000 \,J$
