Waist
Every body's got a Waist

Yes, we're anthropomorphizing again. Most fretted instruments have a waist, the narrow part of the body between the hips and shoulders:
Actually, we don't call the lower bout the "hips" but we do often refer to the upper curve of the upper bout as the "shoulder."
This 19th Century guitar has a very pronouced waist. Compare it to the waist of a Dreadnought.
