Question: what is it called when a girl has her first period?
Answer: Menarche (/mɪˈnɑːrkiː/ mi-NAR-kee; Greek: μήν mēn "month" + ἀρχή arkhē "beginning") is the first menstrual cycle, or first menstrual bleeding, in female humans. From both social and medical perspectives, it is often considered the central event of female puberty, as it signals the possibility of fertility.