Plain English Meaning
An airplane that has a small wheel under its nose and two main wheels further back. Because of this layout, the airplane sits flat on the ground and the pilot can see straight ahead while taxiing.
Full Definition
An airplane with tricycle landing gear, in which the third wheel is located under the nose of the aircraft and the two main wheels are positioned behind the airplane's center of gravity. This configuration causes the airplane to sit level on the ground and gives it forward visibility over the nose during taxi, takeoff, and landing.
Context Anchor
Seen in taxiing, takeoff, and landing discussions, especially when comparing how airplanes behave on the ground.