Why does grandma call her daughter's children nephews?

Grandma calls her daughter's children nephews because: the grandson happens to be my uncle's nephew, my uncle is my grandmother's son, and my grandmother is called after her son. There are many local appellations among the people: mother follows son and wife follows husband. For example, Pan Jinlian in Water Margin is called Uncle Song Wu (originally his brother-in-law).

In the tradition of northern rural areas, even grandparents will not call their daughters' grandchildren, but nephews. In the past, there was a saying in the countryside that "a married girl is spilled water", thinking that a girl would not be her family after she got married. Especially in ancient times, married women often took their husbands' surnames, and "grandchildren" could only be used by their families. The so-called nephew also refers to children born with a foreign surname, and even has a considerable gap with their grandchildren in terms of treatment.