Behind closed doors phrase
If something is done behind closed doors, it is done privately or secretly, or with no audience or crowd watching
I don't care about what is happening behind closed doors. It's none of my business.
A: Lisa and Andy have just got divorced. I thought they were an absolutely perfect family. B: You never know what happens behind closed doors.
They are negotiating the contract behind closed doors.
I'm afraid that the UEFA Euro 2020 will be held behind closed doors because of the Covid-19 outbreak.
Used to tell someone to keep secret what you're about to say
The room you are currently in.
To be secretly working together
When two individuals desire to be alone with each other, a third person is not welcome.
The phrase is hyphenated when being used before a noun.
They held a behind-closed-doors conference.