What does "closed door" mean?

Not open to participation by non-members or the public.

Closed door

adj

adj ·Rare ·Advanced level

Adjective

1
Not open to participation by non-members or the public. not-comparable
"The leaders held a closed door meeting to decide on a future course of action in the case."

"The leaders held a closed door meeting to decide on a future course of action in the case."

Metaphor of an isolated room, behind doors that are closed.