Plain English Meaning
An airplane that has a small wheel under the nose plus two larger wheels under the wings or fuselage, so it sits flat on the ground rather than tail-down.
Full Definition
An aircraft with a tricycle landing gear arrangement consisting of two main wheels positioned aft of the center of gravity and a single steerable wheel located under the nose, forward of the center of gravity. This configuration causes the aircraft to sit level on the ground and is the most common landing gear layout on modern light aircraft.
Context Anchor
Seen in weight-and-balance discussions when explaining how the aircraft’s load is shared between the nosewheel and the main wheels while the aircraft is on the ground.