Perm
A chemical treatment that sets curls or waves into the hair, lasting until it grows out.
Also: permanent wave, body wave
A perm, short for permanent wave, breaks and re-forms the bonds that give hair its shape. The hair is wound onto rods, a waving solution is applied to break the bonds, and then a neutraliser sets them in the new curled shape. Big rods give loose waves, sometimes called a body wave; small rods give tight curls. Early machine perms of the 1900s used electric heat. The curl stays in the treated hair until it is cut off, though new growth is straight.