Master keying is a system that allows multiple locks to be opened using a single key, known as the master key. It provides convenience and enhanced security for buildings with multiple locks and various access levels. In a master key system, each lock has its unique key called a change key, which can only open that specific lock. The master key, on the other hand, has the ability to open multiple locks within the system. This is achieved through a complex arrangement of pins and cylinders within the locks, which are designed to align with both the change key and the master key, enabling them to operate different locks within the system.