Maybe it's an old school/new school thing, but I've been hearing the term seg height applied in a few different ways. When it comes to progressive lenses, is seg height defined and most commonly used as the distance between the center of the pupil and the bottom of the lens? Or is seg height the beginning of the progressive addition on a progressive lens? What is the most commonly used term for the distance between the pupil and bottom of the lens in a progressive lens?

Thanks!