A nephew is the son of your sister or brother. This makes you the aunt or uncle of that nephew.
While a mom, dad, sister, and brother are members of an immediate family, a nephew is part of your extended family because he's the son of a sibling. When brothers or sisters have male children, you become an aunt or an uncle to a nephew. If your nephew has a sister, she is your niece. Both niece and nephew originally meant "grandchild," but narrowed to their current meanings in the 1600s.
