1, mother's youngest sister. It always means "minimum" here. Generally speaking, it is when there are many brothers and sisters in the family, such as four aunts, two aunts, three aunts and old aunts (that is, young aunts, which will be called "old" at this time).

In the north (especially in the northeast), the mother's youngest sister is called "old aunt". In some places in Hebei, father's menstruation is called menstruation.