A polite/honorific term for someone else's nephew (often used as '甥御さん').
社長の甥御さんが新しいプロジェクトに参加します。
The company president's nephew will join the new project.
甥御さんはサッカーがとても上手ですね。
Your nephew is very good at soccer, isn't he?
明日は甥御さんの卒業式ですか？おめでとうございます。
Is your nephew's graduation ceremony tomorrow? Congratulations.