Definition
The lowest steady engine speed, expressed in revolutions per minute, at which the engine continues to run reliably with the throttle fully retarded. At idle rpm, the engine is producing minimum power, just enough to keep itself running and to drive accessories.
Plain English
The slowest the engine turns when you pull the throttle all the way back without it stopping. It's the engine's quiet, low-power setting on the ground or during a power-off descent.
Context Anchor
Pilots encounter idle rpm during engine checks, taxi, power-off practice, approaches, and landing discussions where low engine power affects thrust and airplane handling.
Derivation
Idle' comes from Old English idel, meaning 'empty' or 'doing no work.' An idling engine is running but not doing useful work in terms of producing thrust. 'RPM' stands for revolutions per minute -- how many full turns the crankshaft makes each minute.
Why Pilots Care
Correct idle RPM prevents rough running, flameouts, or excessive wear during ground operations and provides the baseline for power management.
Intuition Check
Do not read idle as off. At idle rpm, the engine is still turning and may still produce a small amount of thrust.
Example Sentence 1
After landing, the pilot pulled the throttle back to idle rpm and let the airplane slow down before turning off the runway.
Example Sentence 2
After landing the pilot reduced power to idle RPM while taxiing back to the ramp.