Change key=a key cut to open a single lock in a master keyed series of locks. Master key=a key cut to open more than one lock in a master keyed series of locks. He means that they someone lost the key for cabinet A so they gave the user of cabinet A a master key so they could still get into the cabinet. Whenever someone lost a key to a particular cabinet they just gave them a copy of the master.
This is one of the reasons why lockmiths advise you to change your master key system every 10 years or so. This kind of thinking happens everywhere, especially in the property management field. Heck, I've worked at hotels and universities where the housekeeping staff had a grandmaster key simply because the person in charge of key control (the in-house "locksmith") didn't know how to repin a lock or how to decode a cylinder. And yes I have seen one university where the "locksmith" didn't know how to repin a cylinder...He just ordered a new cylinder from Best, combinated to the master key. His explanation was that this way he didn't have to worry about whether the people with master keys could still get into the room/cabinet/padlock with their master key.
