What would NOT be considered a leg in flight terminology?

In flight terminology, a "leg" refers to a portion of a flight journey that encompasses travel between two points. This can typically be a direct flight between two cities or segments where a passenger changes planes or stops at an intermediate point.

Given this understanding, a flight cancellation due to weather conditions does not constitute a leg of a flight. A flight cancellation means that the planned travel segment is no longer taking place, therefore it cannot be identified or defined as part of a journey.

The other options clearly fit within the definition of a flight leg. A flight from New York to Chicago represents a direct leg; a stopover in Dallas indicates that there are segments of the journey both to and from this stop; and a part of the flight crew's assignment relates to managing the operational aspects of each leg. Thus, only the cancellation is explicitly outside the bounds of what defines a leg in this context.