Menstruation is the shedding of the uterine lining through the vagina. Menstruation occurs on average once a month, for 4 to 7 days. This is also commonly called your "menstrual period," or just your period. In online forums, menstruation is sometimes referred to as AF (Aunt Flo).
During the 2-week wait (the time between ovulation and your expected period), the corpus luteum secretes the hormones progesterone and estrogen. This hormone signals the uterine lining to grow and prepare for implantation of a fertilized egg, or embryo. If a fertilized egg doesn't implant itself in to the uterine lining, the hormones estrogen and progesterone drop. This drop leads to the deterioration of the lining of the uterus, which then leads to menstruation.
The first day of your menstrual period is considered to be the first day of the next cycle.
