- 1a (1): The natural cessation of menstruation occurring usually between the ages of 45 and 55 with a mean in Western cultures of approximately 51. (2): The physiological period in the life of a woman in which such cessation and the accompanying regression of ovarian function occurs--called also climacteric.
b: Cessation of menstruation from other than natural causes (as from surgical removal of the ovaries).
Definition from: Merriam-Webster's Medical Dictionary by Merriam-Webster Inc.
See also Understanding Medical Terminology.