Menstruation — a part of the monthly menstrual cycle.
They occur in the body of girls and women on the eve of a possible pregnancy. Each month, an egg is released from the ovary during ovulation. At the same time, the lining of the uterus thickens in preparation for pregnancy.
If fertilization doesn’t occur, the lining of the uterus is rejected as bleeding (menstruation) and the cycle is repeated.