Definition 1 of 2
Definition
The controlled movement of an aircraft on the surface of an airport under its own power, excluding takeoff and landing. Taxi includes movement on taxiways, ramps, and other airport surfaces, and for helicopters operating without ground contact at airports with movement areas it also includes air taxi and hover taxi operations.
Plain English
Driving the aircraft along the ground at an airport using its own engine power, getting from where it is parked out to the runway, or back from the runway to parking. For helicopters, it also covers low, slow movement just above the ground when the situation calls for it.
Context Anchor
You will see and hear this word in airport ground operations, especially when asking ground control for instructions or moving between parking and the runway.
Derivation
From the older sense of a 'taxicab' moving slowly through streets to pick up or drop off. Aviation borrowed the word in the early 1900s to describe an aircraft moving slowly under its own power on the ground, much like a cab making its way through traffic before reaching open road.
Why Pilots Care
Correct taxi procedures prevent runway incursions and keep ground movement safe and orderly.
Intuition Check
Taxi does not mean a car service here. In aviation, it means moving the aircraft on the ground under its own power.
Example Sentence 1
After completing the run-up, the pilot called ground and was cleared to taxi to Runway 18 via taxiway Bravo.
Example Sentence 2
After landing, the aircraft taxied slowly to the ramp for parking.