Hi Kay,
I don't have an answer, I'm just here to muddy the waters.

I always assumed that a woman's waist was the narrowest part of her torso. Mine is above my navel. (In fact, I take measurements at my waist, belly button, "bagel" (gut), and hips -- 4 different places.)

My much-younger sister laughed at me a couple of years ago because the waist of my jeans was so high. (I was wearing an old pair of Lee's.) I told her that, believe it or not, women's jeans used to be made to sit at the waist. She told me that her waist was at her belly button and I was "shortwaisted like Mom." (Our mother's waist is right under her breasts; mine is not.)

My sister and I debated without consensus. I maintain that where your actual waist sits is a physical fact and that fashions my fall above, at, or below it, but your waist will always be in the same place. My sister feels that the fit of her (always stylish) jeans dictates where her waist is at the moment.