Many people misunderstand the term "masterkeyed".

Just because several different locks work on the same key doesn’t nesessarily mean the locks are masterkeyed. They may be simply "keyed alike".

Masterkeyed means that several locks, that each have individual keys, also all operate one common "masterkey".

Take for example, a hotel. One key (the "master" key) will open every lock in the hotel - front entrance, office, guest rooms - while each room has its own individual ("day" key) key that only opens that particular door.

More elaborate systems can include options like having all the guest room keys operate common areas, such as the pool, game room, and exercise room. The system can even be set up with "sub-master" keys, allowing housekeeping to carry only one key for each floor.

While master key systems can provide a convenience for the user, they must be properly maintained by a qualified locksmith to ensure the continued integrity and security of the system. If any locks in the system are rekeyed without the availability of the proper paperwork ("pinning charts"), key interchanges ("cross-keying") can result, allowing a key to operate other locks in the system, that it is not intended to operate.