Airspace (noun)

1. The portion of the atmosphere above a particular area, especially above a country and subject to its jurisdiction.
2. The area above a certain altitude in which aircraft are permitted to fly.

Origin:

Early 20th century: from air + space.

Examples:

1. The airspace above a country is regulated by its aviation authority.
2. The airspace was closed due to the danger posed by a volcanic ash cloud.
3. The airspace over a city is busy with commercial and private aircraft.
4. The airspace is divided into different classes based on the altitude and type of aircraft using it.
5. The airspace near an airport is carefully monitored to ensure the safety of aircraft.