airspace

Short definition from Wiktionary

Noun

1. 1
   A specified portion of the atmosphere, especially that under the technical aviation control and/or jurisdiction of a particular state over which territory (and territorial waters) it lies.
2. 2
   that part of the sky designated for the sole use of aircraft.
3. 3
   Space (i.e. a few neighboring frequencies) available for broadcasting within a particular frequency band.
4. 4
   The portion of an enclosed area which contains air, especially breathable air.
5. 5
   The cavity in a cavity wall containing air for insulation.