The “Volt-Ampere” is the measure of “apparent power” and is used primarily in circuits using alternating current (AC).  The Volt Ampere (VA) consists of 2 components, the first is the real power known as Watts, while the other is the reactive power known as VAR (Volt-Amps-Reactive).  The following equation shows how the 3 terms are related:  VA = (W² + VAR²)^1/2.  In DC circuits, the VAR term drops to 0 since reactive power doesn’t show up in DC.  More information on this topic can be found here

A common graphical representation of the relationship between these three components is the power triangle.  The real power (Watts) makes up the adjcent leg, reactive power (VAR) makes up the opposite leg, and the apparent power (VA) is the resulting hypotenuse.