Passe-partout is a noun meaning a master or skeleton key, an ornamental mat for a picture, or a method of framing in which a piece of glass is placed over a picture and is affixed to a backing by means of adhesive strips of paper or other material pasted over the edges. NOTE: This word has a few more meanings then what is listed here but I truncated it.
A passé-partout with a cryptic note was taped to Brenda’s door.