Estrogen is a hormone produced primarily by the ovaries, but also by the adrenal glands and fat cells in both men and women. Synonyms for estrogen include estradiol, estrone, and estriol. Estradiol is the most potent and abundant type of estrogen, while estrone is the most prevalent estrogen in postmenopausal women. Estriol is a weaker estrogen produced during pregnancy. Other synonyms for estrogen include oestrogen, 17 beta-estradiol, and E2. Estrogen plays a crucial role in regulating the female reproductive system and bone density, and has been linked to the development of breast and uterine cancer in some cases.