Definition
The propeller blade setting in which the blades are rotated to a steep (high) angle relative to the plane of rotation, causing the propeller to take a larger 'bite' of air per revolution. This larger bite increases the load on the engine, which results in a lower propeller and engine rpm. It is used during cruise and descent phases of flight where efficient, low-rpm operation is desired.
Plain English
The propeller blades are turned to a steep angle so they grab a bigger chunk of air with each turn. Because each turn does more work, the propeller spins more slowly. Pilots use this setting for cruising along, not for takeoff or climb.
Context Anchor
You encounter this when using the propeller control in an airplane with a constant-speed propeller, especially when reducing rpm after takeoff or setting cruise power.
Derivation
Pitch' here comes from the same idea as the pitch of a screw -- how far it would advance through a solid in one turn. A steeper blade angle means a bigger theoretical advance per revolution, hence 'high pitch.' 'Low rpm' simply describes the resulting slower rotation because each turn is now doing more work.
Why Pilots Care
This position improves fuel efficiency, reduces engine wear, and maintains adequate thrust for level flight without operating at high RPM.
Analogy
Think of a bicycle in a high gear. Each push of the pedals moves you a long way, but you can't pedal quickly and you wouldn't start from a stop in that gear. Same idea here: high pitch is the airplane's high gear -- efficient at speed, wrong for takeoff.
Intuition Check
High pitch does not mean the airplane’s nose is high, and it does not mean high rpm. Here, pitch means propeller blade angle: higher pitch normally goes with lower rpm.
Example Sentence 1
Once established in cruise, the pilot moved the propeller control aft to set a high pitch/low rpm position for fuel-efficient flight.
Example Sentence 2
In the high pitch/low rpm position the engine runs cooler and uses less fuel while still producing enough thrust for straight-and-level flight.