Final answer:
Menarche is the term for a girl's first menstruation, marking the start of the menstrual cycle during puberty. It typically takes place between ages 8 and 16 and signifies the female body's readiness for reproduction.
Step-by-step explanation:
A girl's first menstruation is known as menarche, which is a significant milestone in female puberty representing the commencement of reproductive capability. During menarche, the shedding of the inner portion of the endometrium occurs, which is expelled out through the vagina. This process is also generally referred to simply as menstruation or monthly periods, and it signifies the start of the menses phase of the menstrual cycle. In the United States, menarche typically occurs around the average age of 12.5 years, but it can vary anywhere between eight and 16 years, influenced by genetic and environmental factors like nutrition.
Menarche marks the beginning of the menstrual cycle, a physiological cycle that prepares the female body for pregnancy. The first occurrence of menarche is a momentous event and is often celebrated or noted as a coming-of-age ritual in various cultures. Understanding menarche is crucial for young women as it is a core aspect of health education, signaling the body's development and reproductive health.