Nullification ("nullo") is the voluntary removal of body parts. Most commonly this means castration (and sometimes penectomy), amputation of fingers or toes, or, in extreme cases, removal of full limbs. Sometimes it may also mean the removal of nipples or teeth.
At first glance this may appear to be a deep psychiatric problem, but modern psychiatry is begin to recognize it as something more valid. To oversimplify, a person has an internal body image -- this body image may not include all the normal body parts. If not, they will not be happy until they line up this internal image with the real world. Nullification may be the answer in some of these cases.