Chaloupes comes from the verb chalouper, which means to sway or wobble, often like a boat. It's a less common verb that evokes a very specific kind of movement.
In the song, the lyric "Comment tu chaloupes?" (How do you sway?) refers to the way the person moves, likely in a sensual, rhythmic dance. It paints a vivid picture of their graceful, almost undulating motion, making it a captivating word choice.
"La nuit nous appartient" is a slow, sensual song about two people losing themselves in each other once darkness falls. Bernard Lavilliers describes the moment night arrives and a woman moves close to him, her perfume swirling around them as they sway together.
Most of the song is him watching her and wondering what she's really thinking. Her half-smile hides something he can't quite read, and he asks what she's imagining for their near future. Her dress turns with every step, her shoulders following the motion, and for a moment nothing else exists but the two of them moving as one.
By the end, that uncertainty turns into a quiet certainty. They step out from the crowd because they've become inseparable, and the title becomes a simple statement: whatever happens once daylight returns, right now the night is theirs alone.