Refers to any of the hair below the skin surface, but is often used to refer to that portion of the hair follicle that must be destroyed to prevent regrowth.

the part of the hair buried in the follicle under the skin.

The portion of a hair that extends from the skin's surface to the hair bulb.

The part of the hair contained within the follicle.

The portion of the hair that stretches from the surface of the skin to the hair bulb.