With a slightly different spelling it's the cut out inside a picture frame -kind of like the frame for the picture within the frame. I can't remember where else I have seen it but I think it might be in the comics (OPUS?) but, I can't remember where for sure.
I did indeed hijack my TUG username from a character in 'Around The World In 80 Days' (1956), the manservant who accompanied Phineas Fogg on his journey. I thought it fitting as one who accompanies my DW on our travels.
French for 'goes everywhere', generically, a passepartout is a skeleton key that opens any lock or the French term for the mat, usually cardboard, that both serves to frame a piece of art in a frame and to hold the art from contact with the glass of a picture frame.
The play we saw changed his name to Phileas Fogg. The woman had a major role, which I guess in the movie did not. The play focused on the time it took to travel, not the methods. So now I am anxious to watch the old movie again. Saw it as a kid and have some vague memories.
In the original (the Jules Verne novel) and the 1956 grand extravaganza movie, it is Phileas Fogg. There is at least one other movie adaption, a number of Amazon reviews, etc., however, that made Phineas Fogg the main character. Who knows why? My guess is that someone screwed up and it stuck.