passe-partout

/P AE0 S EY1 P AA1 R T AW0 T/
noun
  1. 1

    That by which one can pass anywhere; a safe-conduct.

  2. 2

    A master key.

  3. 3

    A light picture frame or mat of cardboard, wood, etc., usually put between the picture and the glass, and sometimes serving for several pictures.

Source: https://en.wiktionary.org/wiki/passe-partout