Sister-in-law refers to the address of brothers to each other's girlfriends or daughters-in-law. For example, both of them are 30 years old, but the older person's girlfriend or daughter-in-law is in her early twenties, so the young man will call his brother's daughter-in-law "little sister-in-law".

Address refers to the address forms that people use in daily communication and entertainment. In interpersonal communication, choosing the correct and appropriate address reflects one's upbringing, the degree of respect for the other party, and even the development of the relationship between the two sides and social fashion, so it can't be used casually.