The interior or inside of something — the internal area or structure (of an organization, device, place, etc.).
工場の内部は安全ヘルメットが必要だ。
Inside the factory you need a safety helmet.
問題の原因はそのシステムの内部にある可能性が高い。
There is a high possibility that the cause of the problem lies within the system itself.
建物の内部を見学させてもらった。
I was allowed to tour the inside of the building.