What is mensturesion?

It seems like there might be a typo in your question. If you meant "menstruation," it refers to the monthly biological process in which the uterus sheds its lining when pregnancy does not occur, resulting in bleeding from the vagina. This typically happens in females of reproductive age and is a key part of the menstrual cycle, which is regulated by hormonal changes. If you meant something else, please clarify!