"Uncle" is the address for the mother's elder sister or younger sister's husband. They are elders. "Uncle" can also be called "Aunt Dad". In our hometown, we call it "aunt's son" directly. But if you write the name "aunt's son", it seems to be in Mandarin that the older generation will become grandparents.

"Uncle" is a title between sister husband and peers. It's like "sister-in-law" is the address between brother and wife. In other words, a woman doesn't have an uncle, just as a man can't have a sister-in-law. I am a woman, how can I have an "uncle"? If I want to call my sister's husband, I can only call him "brother-in-law" or "brother-in-law", just as a man can only call his brother's wife "sister-in-law" or "sister-in-law". Of course, a woman can also call her brother's wife "sister-in-law" or "sister-in-law".

"Uncle" is only spoken, and the written language should be called "brother-in-law". It is precisely because of this written language that in many places, there is no such colloquial address as "uncle" as "brother-in-law", and "uncle" and "uncle" are widely used.