Plain English Meaning
It is the FAA's official rulebook for how to design an airport — how wide runways should be, how far apart taxiways should sit, how much clearance areas need, and so on. When the FAA refers to airport design standards, this is the document they mean.
Full Definition
An FAA Advisory Circular titled 'Airport Design,' which provides standards and recommendations for the geometric layout and engineering design of airports, including runways, taxiways, aprons, and related facilities. It is the primary reference document used by airport designers and the FAA to determine dimensional standards based on the aircraft expected to use the airport.
Context Anchor
Seen in AIM glossary references, airport planning documents, and discussions about runway, taxiway, and airport - design standards.