Hair growth refers to the process by which hair is produced on a person's body. It involves the growth of new hair cells from follicles, which are tiny structures found in the skin. Hair grows at an average rate of about 1/2 inch per month and has different stages such as active phase (anagen), catagen, telogen, and exogen phases. Factors that influence hair growth include genetics, hormones, nutrition, stress levels, medications, and overall health.