In French `` Belle de Jour '' means `` beauty of ( the ) day , '' as opposed to `` femme de nuit '' or `` belle de nuit , '' women of the night ( common references to prostitutes ) . In French `` Belle de Jour '' is an expression translating literally as `` beauty of ( the ) day , '' as opposed to `` femme de nuit '' or `` belle de nuit , '' women of the night ( common references to prostitutes ) .