internal door; inner door
Refers to a door located inside a building or structure, as opposed to an exterior door. Often used in architectural or descriptive contexts.
この建物の内扉はすべて木製です。
All the internal doors in this building are made of wood.
内
When I opened the inner door, there was a spacious living room.
A compound of 内, “inner,” and 扉, “door,” referring to an interior or inner door.