A 外甥 (wàishēng) refers to one's nephew, the son of one's sibling.
外甥 (wàishēng) cheat sheet for homework
侄子 (zhízi): A 侄子 (zhízi) is another term for nephew, but specifically refers to the son of one's brother.
姪女 (zhínǚ): 姪女 (zhínǚ) is the term for niece, which refers to the daughter of one's sibling.
舅舅 (jiùjiu) means maternal uncle, who is the brother of one's mother.