noun
deputy leader; vice leader; second-in-command
Used in organizational contexts (teams, projects, clubs) for the person who assists or substitutes for the leader.
彼はプロジェクトの副リーダーに任命された。
He was appointed deputy leader of the project.
リーダーが不在のときは副リーダーが指揮をとる。
When the leader is absent, the deputy leader takes charge.