A Cousin
Your daughter is your brother's niece. Your brother is your daughter's uncle
Your brother's daughter has a daughter? That is a great niece.
Your brother's daughter is your niece. Her daughter is your great niece.
Your brother's daughter and your daughter are first cousins to each other. Your brother's daughter and your daughter's daughter (your granddaughter) are first cousins, once removed, to each other.
Your brother or sister's daughter is called 'your niece.'
Your brother's sister is your daughter's aunt, and your daughter is your brother's, and his sister's, niece.
your brother's daughter is you niece
The daughter of your husband's brother is his (and your) niece. Her daughter is his (and your) great niece.
brother's daughter relation
You brother's daughter is your niece, just as your sister's daughter is your niece. The English language does not have different terms for daughter of brother and sister.
Your sister's daughter and your sister's brother are niece and uncle to each other. The daughter is the niece of the brother and the brother is uncle to the daughter.
Your sister-in-law's husband may be your brother. If so then the brother-in-law is either your husband, in which case the daughter is your daughter; or the brother-in-law is your brother, so the daughter is your niece or the brother-in-law is the brother of another sibling's spouse, in which case the daughter is still your niece If your sister-in-law's husband is not your brother, then he is not related to you and his brother-in-law's daughter is not related to you.