What is the term used to describe an aircraft's current flying altitude above sea level?

The term that describes an aircraft's current flying altitude above sea level is referred to as "Pressure Altitude." This measurement represents the altitude of the aircraft when adjusted to the standard atmospheric pressure of 29.92 inches of mercury, which is a standard reference point used in aviation. Pressure altitude is crucial for determining aircraft performance, navigating, and ensuring safe separation between aircraft in the airspace.

The other terms represent different concepts: "Flight Level" refers to the altitude of an aircraft expressed in hundreds of feet, indicating that the altitude is determined by a standard atmospheric pressure setting. "Ground Level" describes the altitude in relation to the surface of the Earth, which may vary based on topography and is not a standard reference for flying. "AGL," or Above Ground Level, measures altitude in relation to the ground directly below the aircraft, also lacking the uniformity of Pressure Altitude, which is consistent across all regions.