Definition
The official document, produced by the aircraft manufacturer and approved (in part) by the FAA, that contains the operating limitations, procedures, performance data, weight and balance information, and systems descriptions specific to a particular aircraft by make, model, and serial number. The POH is the manufacturer-published handbook used as the practical pilot reference; the AFM is the legally required, FAA-approved flight manual that must be carried in the aircraft. For most modern general aviation aircraft, the two are combined into a single document referred to as the POH/AFM.
Plain English
It's the book for your specific airplane. It tells you how to operate it, what its limits are, how it performs, and what every system does. Part of it is legally required to be in the aircraft when you fly.
Context Anchor
Pilots use the POH/AFM before and during flights when checking speeds, equipment, fuel planning, runway distance, loading, and emergency actions for that exact airplane.
Derivation
“Pilot's Operating Handbook” means a handbook written for the pilot who operates the airplane. “Airplane Flight Manual” is the more formal FAA term for the approved flight manual. The combined term POH/AFM is used because many modern airplanes have the information in a POH format while still containing FAA-approved AFM sections.
Why Pilots Care
Regulations require that the pilot in command operate the aircraft in accordance with the POH/AFM, making it the primary legal and practical reference for that specific airplane.
Intuition Check
Do not treat a POH/AFM as a general flying textbook. It is the official operating reference for a particular airplane, and the details can change from one model or serial number to another.
Example Sentence 1
Before the cross-country flight, she opened the POH/AFM to the performance section to calculate takeoff distance for the density altitude that day.
Example Sentence 2
During the engine failure after takeoff, the pilot referred to the POH/AFM emergency checklist for the correct airspeeds and procedures.