What is engine-out taxi out time? What is engine-out taxi out time?

a) The time between the first movement of the aircraft under its own power and the start of the last engine

b) The time between the first movement of the aircraft regardless if it's being pushed back without any engines running and the start of the last engine

And one additional question - how would you define the the start of the last engine?

a) The moment the fuel valve is opened

b) The first moment the engine is running (stable N1, fuel flow, oil pressure and temperature, etc.)

c) Something else
It's the time taxiing without engines on, for example when under tow or during push back. As opposed to when you're taxiing under the aircraft's own power

The second is potentially subjective, but I'd personally count it as the moment the engine is actually running, post-start up procedure: that's the moment when I could use the engine as an actual engine with useful power.