airspace

noun

• 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."

• That part of the sky designated for the sole use of aircraft.
• 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."

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