Phillumenists use skillet to describe a pre-printed, pre-cut, pre-scored, piece of cardboard intended to be formed into an outerbox of a matchbox. However, the match industry uses skillet in a more general sense to mean any pre-cut piece of veneer or card that is a part of a matchbox. Therefore skillet can mean a pre-cut piece of flat card or wooden veneer that is folded into the outerbox of a matchbox whether or not it has been printed or whether or not it will have a label affixed. Skillet can also mean the single flat cut piece of card or pieces (rim and bottom) of veneer or card that an innerbox is made from.
It is not possible to unfold a skillet, for as soon as a skillet has been folded it can never revert to being a skillet. Therefore there can be no such thing as a flattened skillet.