The phrase "sister daughter" implies a relationship between two people, where one is the sister of the other's parent. To express this relationship clearly, you could say:
* Niece: This is the most common and direct way to describe someone who is your sister's daughter.
* Your sister's daughter: This is more literal but less concise than "niece."
* [Sister's name]'s daughter: This is specific and avoids ambiguity if you have multiple sisters.
For example, if you are talking about your sister's daughter, you would say:
* "My niece is visiting this weekend."
* "Your sister's daughter is a talented artist."
* "Sarah's daughter is starting school this year."