Skeleton key

A skeleton key (also known as a passkey[1]) is a type of master key in which the serrated edge has been removed in such a way that it can open numerous locks,[2] most commonly the warded lock.

The term derives from the fact that the key has been reduced to its essential parts.

This can usually be done by removing most of the center of the key, allowing it to pass by the wards without interference, operating the lock.

To counteract the illicit creation of such keys, locksmiths can put wards not just in the center but on the outside as well, making the creation of a skeleton key more difficult.

In hotels without electronic locks, skeleton keys are used by housekeeping services to enter the rooms.

A padlock skeleton key with all of the teeth filed down (right) and a normal key (left) for the same lock. The normal key on the left will open only the lock that it goes to, but the skeleton key on the right will open any lock with this particular keyhole.
Two warded lock keys and a homemade skeleton key
A common set of skeleton keys used to open most types of warded padlocks