Airspace

noun

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.

   "Various European countries transferred the aviation control of their adjoining airspace to Eurocontrol, while each retaining legal jurisdiction."

2. That part of the sky designated for the sole use of aircraft.
3. Space (i.e. a few neighboring frequencies) available for broadcasting within a particular frequency band.

   "The legalisation of free radios caused a bitter fight for airspace."

4. The portion of an enclosed area which contains air, especially breathable air.
5. The cavity in a cavity wall containing air for insulation.