Operational Excellence is the state in which stable, improving operations are the norm — where deviations become visible and are handled systematically by the organisation itself, without depending on individuals or external consultants.
Where Lean is a collection of principles and methods, Operational Excellence describes the result: an operation that runs stably, discovers its own problems and improves itself. It requires three layers: visibility (metrics and boards), routines (Daily Management) and behaviour (management that responds to deviations rather than firefighting).
The test is simple: does the operation still run when the key person is on holiday? If the answer is no, the operation is carried by people, not by systems.
Operational Excellence is not a state you reach once and keep. It is maintained by the same routines that created it, and it slips back as soon as the follow-up stops. Maturity is therefore best measured by what still works a couple of months after an improvement effort ends, not by how it looked on the final day.