Definition
A turbine engine power setting used during ground operations in which the engine runs at the lowest steady RPM needed to move the aircraft on the ground or to keep the engine operating while stationary. It is the low end of the engine's operating range, producing minimal thrust but enough to taxi the aircraft or sustain accessory and system loads.
Plain English
The lowest engine power setting used while the aircraft is on the ground -- just enough to roll along taxiways or sit still with the engine running.
Context Anchor
Seen in engine operating procedures, taxi checklists, and power-lever or throttle instructions during ground operations.
Derivation
Taxi' comes from aircraft moving slowly on the ground like a taxicab moving through city streets. 'Idle' originally meant 'doing nothing,' and here describes the engine running at its lowest useful speed -- not stopped, but not producing meaningful thrust.
Why Pilots Care
Setting and maintaining a proper taxi/idle power keeps ground speed manageable, protects the brakes from overheating, and avoids blasting people, equipment, or other aircraft behind with excess jet exhaust.
Intuition Check
Taxi/Idle does not mean the engine is off or doing nothing. It means the engine is running at a very low power setting for safe ground movement.
Example Sentence 1
After landing and clearing the runway, the crew set the engines to taxi/idle for the trip to the gate.
Example Sentence 2
Maintaining taxi/idle RPM during a long rollout kept the engine temperature within limits.