Final answer:
The rudder is the part of a bird or plane that controls the flight direction by changing the position of a moveable surface on the tail.
Step-by-step explanation:
In the context of birds or planes, the part that controls the direction in which they fly is called the rudder. The rudder is a moveable surface, usually located on the tail of the bird or plane, that helps to change the direction of flight by deflecting air currents. By adjusting the position of the rudder, a bird or pilot can steer the bird or plane left or right.
Learn more about Definition of the word 'rudder' in the context of birds or planes