Plain English Meaning
Everything that makes flying in U.S. airspace work as one connected system: the airspace itself, the airports, the navigation aids, the controllers, the rules, and the equipment that ties it all together.
Full Definition
The network of U.S. airspace, including the air navigation facilities, equipment, services, airports, charts, rules, regulations, procedures, technical information, manpower, and material that supports flight operations within the United States and its territories. It also includes the system's interface with international airspace.
Context Anchor
You will see this term in FAA publications, airspace discussions, flight planning, and any topic involving how aircraft operate within the United States.