What term describes the altitude at which a flight is conducted as indicated by an altimeter?

The term that describes the altitude at which a flight is conducted as indicated by an altimeter is "Flight level." Flight levels are defined as altitudes expressed in hundreds of feet, referenced to the standard altimeter setting of 29.92 inches of mercury (Hg). When an aircraft is flying at a specific flight level, its altimeter is adjusted to this standard pressure setting, which allows for consistent altitude reporting across different regions and weather conditions.

This method of altitude reporting is crucial for maintaining safe separation between aircraft, especially in high-altitude airspace, where varied atmospheric conditions can affect true altitude. Flight levels enable air traffic controllers and pilots to communicate with standardized references that ensure safety and efficiency in operations.

In contrast, "Above ground level" refers to the altitude measured from the ground directly below the aircraft, which can change based on terrain variations. "Mean sea level" is a reference that relates to the average surface level of the ocean, used primarily for altimeter settings but not typically described as an operational altitude in flight. "High altitude" is a relative term without a specific definition in aviation as it can refer to various altitude ranges based on context, but it does not specifically indicate the precise altitude as "flight level" does.