Plain English Meaning
When the nose of the airplane is pressed down so hard during the takeoff or landing roll that the front wheel is doing most of the work and the main wheels are barely touching. The airplane becomes hard to steer and wants to wander off course.
Full Definition
An unstable condition during takeoff or landing in a nosewheel airplane in which most of the airplane's weight is carried on the nosewheel rather than the main wheels, with the main wheels light or off the runway. In this state the nosewheel is steering and supporting the airplane, directional control becomes erratic, and the airplane is prone to swerving, side-skipping, or losing the .