what does "model air" mean?

Question

perhaps something related to aviation management

Answer 1

If you are referring to aviation, the term "model air" does not exist: it is called "standard atmosphere".
That is an "air" that is at 20 deg C, 1013.25 mBars at sea level.
When we fly at what we call "flight level", we are saying we have set our altimeter to 1013mB, even if the air pressure is different.
At lower altitudes, mind you, it is better to use the real pressure (or you might find yourself flying into a mountain!