Nephew — the son of one's brother or sister. Informally '甥っ子' and politely '甥御' are also used.
私には甥が二人いる。
I have two nephews.
甥っ子にお年玉をあげた。
I gave New Year's money to my nephew.
彼の甥は今大学で勉強している。
His nephew is studying at university now.