Many people have a stash of old keys in a drawer or cabinet for "future use." Some keys have been there so long that you no longer remember what they're for. A bike lock? An old car? A cabinet at work? These are Orphan Keys.
"Honey, can we get rid of those stupid Orphan Keys in the strong box?"
"Absolutely not! One of them might open that safe we buried in the back yard during the Nixon administration...if we can find it."