a stabilizer that is part of the vertical tail structure of an airplane

The vertical surface of the tail gives the airplane stability while in flight.

(Also called the "fin.") A fixed vertical surface at the rear of the aircraft to which a movable surface - the rudder - is hinged. The vertical stabilizer helps to stabilize the aircraft in the vertical or yaw axis.

The portion of the tail that provides side-to-side stability. The hinged portion of the vertical stabilizer is called the rudder. Wing—The large, horizontal surface that creates lift (the force that carries a plane into the sky) as it moves through the air.

The vertical stabilizer or fin of an aircraft is typically found on its tail, generally pointing straight upward. It is also known as the vertical tail, and is part of an aircraft's empennage. The trailing end of the stabilizer is typically movable, and called the rudder; this allows the aircraft pilot to control yaw.