What describes a flight that is operating behind schedule due to various reasons?

A flight that is operating behind schedule due to various reasons is referred to as a delayed flight. This terminology is commonly used in the aviation industry to indicate that the flight has not departed or arrived at the expected time. Various factors can contribute to delays, such as weather conditions, mechanical issues, or air traffic control restrictions.

The other terms mentioned represent different concepts within aviation. A circular flight typically refers to a route that departs and returns to the same airport, often with a set itinerary that includes multiple stops. A direct flight means that a passenger travels from the departure airport to the destination without needing to change planes, but it may still make stops along the way. An overnight flight usually describes a flight that departs late at night and arrives at the destination the following morning, often referred to as a "red-eye" flight. Thus, these options do not convey the notion of a flight being behind schedule, confirming that delayed flight is the accurate description.