A large, smooth rock was sometimes used by non-professionals to strike and dis-integrate a foot in order to prepare the SOLE for use later by clients. Male clients in dynastic China then used the SOLE by striking their rocks against the foot. The place where the no-longer-integrated foot made contact with「testicles with foot-no-longer-integrated orifice, raised rod in raised leg orifice.」For folks not deliberately disfigured, the SOLE of the foot is what makes contact with rocks when walking barefooted (not such a good idea, for that very reason).
　FOOT BINDING was:
　「…[T]he custom of applying painfully tight binding to the feet of young girls to prevent further growth. …The process was started before the arch of the foot had a chance to develop fully, usually between the ages of 2 and 5. Binding usually started during the winter months since the feet were more likely to be numb, and therefore the pain would not be as extreme. …To enable the size of the feet to be reduced, the toes on each foot were curled under, then pressed with great force downwards and squeezed into the sole of the foot until the toes broke. The broken toes were held tightly against the sole of the foot while the foot was then drawn down straight with the leg and the arch forcibly broken. The bandages were repeatedly wound in a figure-eight movement, starting at the inside of the foot at the instep, then carried over the toes, under the foot, and around the heel, the freshly broken toes being pressed tightly into the sole of the foot. At each pass around the foot, the binding cloth was tightened, pulling the ball of the foot and the heel together, causing the broken foot to fold at the arch, and pressing the toes underneath. …It was generally an elder female member of the girl's family or a professional foot binder who carried out the initial breaking and ongoing binding of the feet. This was considered preferable to having the mother do it, as she might have been sympathetic to her daughter's pain and less willing to keep the bindings tight. …Qing Dynasty sex manuals listed 48 different ways of playing with women's bound feet」(after removing the binding cloths, of course)
　　[　https://en.wikipedia.org/wiki/Foot_binding 2012-12-17, emphasis ours　]　

Modern definitions (that generally disregard history) …excluding politically incorrect concepts and other meanings deemed offensive today; may list only pigeonholed definitions, euphemisms, or meaningless mnemonics)
Chinese: variant of 蹠
Unihan extended: sole (of the foot)
EDRDG: sole of the foot