Stacking orgasms refers a method for causing what is commonly referred to as "Multiple Orgasms" which involves bringing a woman as close to orgasm as possible so that her body "stores" that orgasmic energy - do this multiple times so that when she finally does have an orgasm she's releasing the energy of five (or more) orgasms simultaneously. Women are capable of having several different types of orgasms including but not limited to vaginal; clitoral; fully body; anal; G-spot; combined & psycholagnic. What's normally refered to as "multiple orgasms" usually combines psycholagnic with any of the other types.
Stacking orgasms can sometimes be difficult if the girl has no clue what you're doing (which she shouldn't) because she gets SO CLOSE just before you back off a bit - sometimes they get angry because they think you're "screwing them up" so they CANT orgasm. They typically think this is what's happening until they find themselves STILL experiencing orgasm for several minutes after you've taken your hands (and everything else) off of them - there is no physical contact at this point; they are STILL experiencing orgasm. This is what "Stacking Orgasms" refers to. There is a SECRET to how it's done! (if you don't know - I'm not going to tell you).