Inédit translates to "unprecedented" or "original." It's a sophisticated word that suggests something new, never before seen or published.
In the context of the song, Serge Gainsbourg laments not being able to preserve "la fraîcheur de l'inédit" (the freshness of the unprecedented/original) from his childhood drawings. This word beautifully captures the unique and irreplaceable quality of youthful creativity and innocence, making it a poignant and memorable choice.
Serge Gainsbourg was a master of dark, poetic, and often shocking storytelling, and "Marilou Sous La Neige" is a perfect example. The song tells a chilling tale from the perspective of a narrator obsessed with a woman named Marilou. At first, he sees her as an innocent figure, like a character in a bande dessinée (comic strip). He feels a sense of ownership over her, even mentioning copyright laws as if she were his creation.
This possessiveness turns dark when he feels excluded from her "erotic games." Feeling betrayed and sick with jealousy, he decides he must "shorten" her existence. The song's title, which translates to "Marilou Under the Snow," takes on a sinister meaning in the final lines. We learn the "snow" isn't from the sky, but is the neige carbonique (carbonic snow) from a fire extinguisher, revealing the narrator's violent act.