Plain English Meaning
An airplane that sits nose-up on the ground because its two big wheels are up front and a small wheel holds up the tail. This layout makes the airplane harder to keep straight on the ground, so the pilot has to work the rudder pedals more carefully than in a nosewheel airplane.
Full Definition
Airplanes with a landing gear arrangement consisting of two main wheels forward of the center of gravity and a small wheel or skid at the tail. Because the main wheels sit ahead of the center of gravity, the airplane is directionally unstable on the ground and tends to swap ends if not actively controlled with rudder during taxi, takeoff, and landing.