Your sister's daughter is your niece. If you are a woman, you are your niece's aunt; if you are a man, you are your niece's uncle.
Your sister's son is your nephew.
An Aunt.
In English, your father's sister's daughter is your first cousin.
Your father-in-law's sister is your spouse's aunt but is not related to her. Call her by her name.
Your sister's husband is your father's son-in-law.
The sons of your father's sister are your first cousins.
Your father's sister is your, paternal aunt,and your mother's sister is your, maternal aunt.Father's sister is your aunt.
Your father's sister's son (or daughter) is your first cousin.
'Aunt' More informally, she may be called 'Aunty ****'
She is your aunt.
aunt
You don't call your brother's sister your aunt. Your brother's sister is your sister, or you. Your aunt is the sister of your mother or father.
She is your aunt. This is true in most traditions. English does not distinguish between an aunt by marriage (father's brother's wife) or an aunt by blood relation (father's sister).