The time in a woman's life when menstrual periods permanently stop; it is also called the "change of life." Menopause is the opposite of the menarche.

Menopause is defined as the time when there has been no menstrual periods for 12 consecutive months and no other biological or physiological cause can be identified. It is the end of fertility, the end of the childbearing years. (A woman may still, however, be able to become pregnant unless 12 consecutive months have passed without a period.)

A woman can usually tell if she is approaching menopause because her menstrual period starts changing. The medical terms used to describe this time are "peri-menopause", “pre-menopause” and the "menopause transition."

Natural menopause occurs when the ovaries naturally begin decreasing their production of the sex hormones oestrogen and progesterone.

Induced menopause occurs if the ovaries are surgically removed (by bilateral oophorectomy) or damaged by radiation or drugs. Due to the abrupt cutoff of ovarian hormones, induced menopause causes the sudden onset of hot flashes and other menopause-related symptoms such as a dry vagina and a decline in sex drive. Early menopause (before age 40), whether natural or induced, carries a greater risk for heart disease and osteoporosis since there are more years spent beyond the protective cover of oestrogen and progesterone.

A "simple" hysterectomy (when the uterus but not the ovaries are removed) before natural menopause should not affect the production of sex hormones and so not cause menopause (unless the nerves or blood supply to the ovaries is damaged during the hysterectomy).

The timing of natural menopause is variable. In the western world the average age is now 51. Natural menopause can, however, be in a woman's 30s or 60s. Factors influencing the time of menopause include heredity (genetics) and cigarette smoking. Smokers (and former smokers) reach menopause an average of 2 years before women who have never smoked.

There is no relation between the time of a woman's first period and her age at menopause. The age at menopause is not influenced by a woman's race, height, number of children or use of oral contraceptives.

The changes of the menopause transition (peri-menopause) can begin approximately 6-10 years before the natural menopause. This is a time when the levels of hormones produced by the aging ovaries fluctuate leading to irregular menstrual patterns (irregularity in the length of the period, the time between periods, and the level of flow) and intermittent hot flashes (a sudden warm feeling with blushing). Otherchanges associated with the perimenopause and menopause include night sweats, mood swings, vaginal dryness, fluctuations in sexual desire (libido), forgetfulness, trouble sleeping and fatigue (probably from the loss of sleep).