Free testosterone is a term used in endocrinology and medicine to describe the fraction of testosterone in the blood that is not bound to sex hormone-binding globulin (SHBG) or albumin. Testosterone is a hormone produced primarily in the testes in men and in smaller amounts in the ovaries and adrenal glands in women. It plays a crucial role in various physiological processes, including the development of male secondary sexual characteristics, muscle mass maintenance, bone density, and libido.