Plain English Meaning
A propeller with blades fixed at one angle. The pilot cannot adjust the blade angle, so there is only one control for the engine: the throttle.
Full Definition
A propeller whose blade angle is set by the manufacturer and cannot be changed by the pilot in flight. Engine power is controlled with the throttle alone, and propeller speed (RPM) varies with throttle setting, airspeed, and load.
Context Anchor
You encounter this when learning how throttle, airspeed, engine speed, and airplane feel relate to each other in many basic training airplanes.
Derivation
‘Pitch’ here refers to the angle of the propeller blades, similar to the pitch of a screw — how far it would advance through a solid in one turn. ‘Fixed’ means that angle is locked in place, so the pilot cannot change how aggressively the blades bite the air.
Why Pilots Care
The pilot must manage engine speed and airspeed together because there is no way to select a different blade angle for climb, cruise, or descent.
Analogy
A fixed-pitch propeller is like a bicycle with one gear. It can work well, but it cannot change its blade angle to better match every climb, cruise, or descent condition.
Intuition Check
Fixed-pitch does not mean the engine speed is fixed. It means the propeller blade angle is fixed; engine speed can still change.
Example Sentence 1
Because the trainer had a fixed-pitch propeller, the student adjusted engine power using only the throttle and watched the tachometer for the resulting RPM.
Example Sentence 2
During a climb in a fixed-pitch propeller airplane the pilot watches engine speed drop as airspeed decreases.