The term "flight" may be undefined as a specific term, but its usage is consistent as a synonym for "sector" in these cases. The term used in the regulation to define the entire itinerary (as in the case of the YYZ-AMS-ALA incident) would be "journey".

You can see evidence of this in definitions section 2(h) where reference is made to "final destination" and to "connecting flights". If a "connecting flight" should be considered to exist, it stands to reason that a "flight" must exist as a unit component of a larger "journey".