What does a flight number represent?

A flight number serves as a unique identifier for each specific flight operated by an airline. This number is crucial for both passengers and airline operations because it simplifies communication and tracking of flights. It allows travelers to easily refer to a particular flight when booking tickets, checking schedules, or seeking updates on delays or cancellations. Additionally, it helps ground staff and air traffic control manage flights throughout their journey, ensuring a smooth operation.

The other choices do not define a flight number accurately. While the number of passengers on board and the number of crew members assigned to a flight are important operational details, they do not represent what a flight number is. The distance traveled by the aircraft also plays no role in defining a flight number, as that is a separate metric related to the flight's route and duration, rather than its identification. Thus, the unique identifier aspect is a fundamental characteristic of a flight number.