This refers to a method of fitting a key. This is a common method used when one lock from a vehicle provides only part of the information needed to make a complete working key. It usually involves the use of a chart or computer software that helps the locksmith generate a list of the possible keys for the lock(s). The locksmith can then make a series of keys to try. It sounds complicated, and it is. But professional locksmiths know that it can save hours of disassembly work!