Wiktionary
absolute altitude
n. (context aviation English) The vertical distance between the airplane and the surface below.(R:MW3 1976: page=6)
Usage examples of "absolute altitude".
He knew the Firefox's predecessor, the Mig-25 Foxbat, had established an absolute altitude record of almost 119,000 feet, and that the Firefox was intended as being capable of a greater performance.
From so grand a title as Blue Mountains, and from their absolute altitude, I expected to have seen a bold chain of mountains crossing the country.
She swerved her attention to the two main altimeters that read pressure altitude, not absolute altitude like the radar altimeter.