A permanent wave, also known as a perm, is a chemical hair treatment that is used to add curl or wave to straight hair. The process involves the use of solutions and heat to reshape the hair's structure, resulting in long-lasting curls or waves. The treatment can be done on all hair types, but the results may vary depending on the hair's texture, length, and condition. The effects of a perm typically last for several months before the hair returns to its natural texture.