Plain English Meaning
An airplane that flies by using a spinning propeller to pull or push it through the air, instead of using a jet engine.
Full Definition
An aircraft that produces thrust by means of a propeller turned by an engine, rather than by jet exhaust. The propeller's spinning blades accelerate a mass of air rearward, and the reaction to that acceleration moves the aircraft forward. Most piston-engine aircraft and turboprops fall into this category.
Context Anchor
Seen in performance and drag-curve discussions, especially when comparing thrust and power required at different airspeeds.