Hair replacement is a term used to describe the process of using a WIG, or other hairpiece, to replace lost or thinning hair. WIG is a three letter word commonly used to refer to this type of hair replacement. Wigs are often made from synthetic fibers or human hair and can be used to cover baldness or to add volume and length to existing hair. Hair replacement is a popular option for those who suffer from hair loss due to medical conditions, age, or genetics.