What does "Flight Level" refer to in aviation?

"Flight Level" in aviation refers to a standard altitude expressed in hundreds of feet, indicating the altitude of an aircraft above a standard datum, which is typically the pressure setting of 1013.25 hPa (hectopascals) or 29.92 inHg (inches of mercury). This term is used to ensure uniformity in altitude reporting and to help maintain safe separation between aircraft flying at different altitudes.

For example, when an aircraft is at Flight Level 350, it is flying at an altitude of 35,000 feet above sea level, based on the standard pressure setting. This designation helps pilots and air traffic controllers communicate clearly and efficiently about the aircraft's altitude, minimizing the risk of misunderstandings and enhancing flight safety.

The other options do not correctly describe the meaning of "Flight Level." The term does not refer to speed, horizontal distance, or specific times during the flight, which are entirely different concepts within aviation metrics.