Menstruation is normal vaginal bleeding that occurs monthly in women from puberty until menopause, usually starting between ages 11-14 and ending around age 51. The menstrual cycle has four phases - menstruation, the follicular phase, ovulation, and the luteal phase. Menstrual hygiene refers to access to products like pads, tampons, cups, or period underwear to absorb or collect menstrual blood flow.