Airspace is the area of sky above a particular place or country. Just as nations have borders on the ground that mark where one country ends and another begins, they also have invisible boundaries extending upward into the sky. When a plane flies from New York to London, it passes through the airspace of several countries, and each nation controls what happens in the sky above its territory.

Countries take their airspace seriously. Military jets protect it, and air traffic controllers guide passenger planes safely through it. If a foreign aircraft enters a country's airspace without permission, that nation might scramble fighter jets to intercept it, similar to how you might challenge someone walking uninvited through your backyard. Commercial airlines must get clearance to fly through each country's airspace, sometimes paying fees for the privilege.

The word also appears in everyday contexts. When you're working on a project and someone leans over your shoulder, you might feel like they're invading your airspace, meaning they're too close for comfort. Pilots talk about crowded airspace around busy airports, where dozens of planes must be carefully coordinated.