Final answer:
A lack of menstruation is termed amenorrhea, which differs from menarche, dysmenorrhea, and endometriosis. Amenorrhea can result from various factors and marks an absence of the menstrual cycle.
Step-by-step explanation:
The absence of menstruation is termed amenorrhea. This condition can be caused by a variety of factors, including pregnancy, hormonal imbalances, excessive exercise, eating disorders, and certain medical conditions. Amenorrhea is distinct from menarche, which is the first menstrual period in a pubertal female. Dysmenorrhea refers to painful menstruation, and endometriosis is a condition where tissue similar to the endometrium grows outside the uterus, causing pain and potentially affecting fertility. The menstrual cycle consists of phases, with the menses phase being the time when the endometrium is shed through the vagina if fertilization has not taken place. Menopause marks the conclusion of menstrual periods, typically occurring when a woman is around 50 years of age.