Amenorrhea is the medical term for the absence of menstrual periods in women of reproductive age. It can be classified into two types: primary and secondary. Primary amenorrhea occurs when a girl has not started her periods by age 15, while secondary amenorrhea refers to the absence of periods for three consecutive months in someone who previously had regular cycles. Several factors can contribute to amenorrhea, including hormonal imbalances, excessive exercise, stress, and certain medical conditions like polycystic ovary syndrome (PCOS) or thyroid disorders. Treatment often focuses on addressing the underlying cause to restore normal menstrual function.