French phrase
Ça reste entre nous.
Meaning
This stays between us.
When to use it
Says that shared information should remain private. Common in an informal promise not to disclose it.
Example dialogue
J'ai une idée pour le spectacle. Ça reste entre nous.
I have an idea for the show. This stays between us.
D'accord, je ne le dirai à personne.
All right, I won't tell anyone.