A skeleton key (also known as a passkey) is a type of master key in which the serrated edge has been filed down so that it can open numerous locks. The term derives from the fact that the key has been reduced to its essential parts. In a broader sense the term can be used synonymously with master key to refer to any key, keycard or other device capable of opening a variety of locks.In US English usage, 'skeleton key' is also occasionally used to mean a standard lever lock key.