Another word for menstruation
is "period." A period is the 2 to 7 days that a girl or woman has her menstrual flow, which is when blood
and tissue leave her body through her vagina.
Why does this happen? Each month, blood and tissue build up in the uterus
to prepare for a fertilized egg in case a woman becomes pregnant. (The uterus
is the place inside a woman's body where a baby will grow.) If the egg
isn't fertilized, that lining leaves the body through the vagina and the
girl or woman has her period.