Menarche is the first menstrual cycle or first menstrual bleeding in female humans. It signals the beginning of fertility potential.
Menstrual Cycle: The monthly cycle of changes in the ovaries and uterus, including menstruation.
Ovulation: The release of an egg from one of the ovaries, typically occurring midway through the menstrual cycle.
Endometrium: The lining of the uterus which thickens during the menstrual cycle in preparation for potential pregnancy.