The concept of reactive power in AC circuits is fundamental for Electrical Engineering.
Here is an explanation:

http://engineering.electrical-equipment.org/energy-efficiency-kvar/reactive-power.html

Apparent power is ordering a beer. Real power is what you want...the liquid. Reactive power is the foam, the stuff that you have to take when you order the beer and it takes up space but leaves you with no satisfaction whatsoever.

Does it matter if it is a lager or stout?

Yes, stouts are not supposed to have a head, they should have a lower pressure (Less bubbles) and higher nitrogen to CO2 mix (Smaller bubbles) than a lager so stouts should be at near 1.0 PF.