The word 'nephew' refers to the son of one's sibling, which means he is the child of either your brother or sister. In family relationships, a nephew is often a young boy or man who is part of your extended family.
The word 'nephew' comes from the Old French word "neveu," which in turn comes from the Latin word "nepos," meaning "grandson" or "nephew." Its usage has evolved over time to specifically refer to the male child of one's brother or sister.