What is the difference between a wig, hair piece, and cranial prosthesis?

Wig is a general term which encompasses a variety of terms to describe the products and to market them. Cranial Prosthesis is a term used to describe a medical necessity need for wearing wig. This terminology is used by companies that provide services for women with medically related hair loss such as alopecia, side effects of chemotherapy treatments, and variety of other medically related hair loss situations.