Learner's definition of ALTITUDE
: the height of something (such as an airplane) above the level of the sea
We're now flying at an altitude [=height] of 10,000 feet.
the air temperature at different altitudes
Some visitors find it difficult to adjust to the city's high altitude.
plants found at higher/lower altitudes [=elevations]
The plane lost/gained altitude rapidly.
flying at low/high altitude
She trained for the race at altitude. [=at a high altitude, where the air is thin]