Menstruation is the monthly shedding of the lining of your uterus. Menstruation is also known by the terms menses, menstrual period, menstrual cycle or period. Menstrual blood — which is partly blood and partly tissue from the inside of your uterus — flows from your uterus through your cervix and out of your body through your vagina.

The menstrual cycle is a term to describe the sequence of events that occur in your body as it prepares for the possibility of pregnancy each month.

The days between periods is your menstrual cycle length. The average length of a menstrual cycle is 28 days. However, a cycle can range in length from 21 days to about 35 days and still be normal.