noun
core member; key member
Refers to a person who is central to a group, team, or organization; often implies strong commitment or influence.
彼はプロジェクトの中核メンバーとして活躍している。
He is active as a core member of the project.
中核メンバーが抜けるとチームは機能しなく
If the core members leave, the team will stop functioning.