Definition: The shedding of the lining of the uterus in women and pubescent girls, typically taking place every 28 days. The lining is made up of tissue and blood, and is needed to nourish a fertilized egg. If there is no fertilized egg, the lining is expelled from the uterus. Menstruation may last between two and seven days. Tween girls typically experience their first period around the age of 12, however it may be years before a girl's cycle becomes regular.
Also Known As: period, your friend, that time of the month, the curse, menstruating