Definition
An uncoordinated turn in which the airplane's tail slides outward from the turn, caused by too much rudder applied in the direction of the turn for the amount of bank being held. The ball in the inclinometer moves to the outside of the turn, indicating excessive yaw rate relative to the bank angle.
Plain English
A turn where the airplane is being pushed around the corner with too much rudder, so the tail swings outward. It feels like the airplane is sliding to the outside of the turn, the way a car skids on a slick road.
Context Anchor
In eights on pylons, skidding can happen if the pilot tries to keep the pylon in position by forcing the nose around with rudder instead of making a smooth, balanced turn.
Derivation
From the everyday word 'skid,' meaning to slide sideways without rolling or steering cleanly -- as a car does on ice. The airplane's tail does the same thing: it slides outward instead of following the nose smoothly through the turn.
Why Pilots Care
A skid raises stall speed on the inside wing and can lead to an unintentional spin if the pilot allows airspeed to decay.
Intuition Check
Skidding does not mean the wheels are sliding on the runway here. In flight, it means the airplane is sliding sideways through a turn because the turn is not balanced.
Example Sentence 1
The instructor pointed out that the student was skidding the turn, and told her to ease off the rudder until the ball returned to the center.
Example Sentence 2
The instructor noted the student was skidding in the base turn and demonstrated proper rudder coordination.