Definition
The controlled movement of an airplane on the ground under its own power, typically between the parking area, runway, and other airport surfaces, using engine thrust for propulsion, rudder and nosewheel steering for directional control, and brakes for speed control and turning assistance.
Plain English
Driving the airplane along the ground using its own engine to get to or from the runway.
Context Anchor
You encounter taxiing any time the airplane moves on the airport surface before takeoff or after landing.
Derivation
From the older sense of 'taxi,' meaning a vehicle that moves at a low, deliberate pace to pick up or drop off. Early aircraft moving slowly along the ground looked like ground taxis, and the word stuck.
Why Pilots Care
Safe taxiing prevents runway incursions, ground collisions, and loss of control during the busiest phase of every flight.
Intuition Check
Taxiing does not mean flying slowly or starting the takeoff. It means moving the airplane on the ground before the takeoff roll or after the landing roll.
Example Sentence 1
After engine start, the pilot began taxiing toward the run-up area, holding the control yoke into the wind.
Example Sentence 2
While taxiing back after landing, the student kept wingtip clearance from other aircraft.