Plain English Meaning
The official books from the aircraft manufacturer that tell the pilot how to fly that particular airplane — how its systems work, what it can and can't do, and what to do in normal and emergency situations.
Full Definition
Manufacturer-produced documents that describe how to operate a specific aircraft safely and correctly, including its limitations, normal and emergency procedures, performance data, weight and balance information, and systems descriptions. For most modern general aviation aircraft, the operating handbook is the Pilot's Operating Handbook (POH), which often also serves as the FAA-approved Airplane Flight Manual (AFM).