What does the "angle of attack" refer to?

The angle of attack specifically refers to the angle formed between the wing's chord line, which is an imaginary straight line that runs from the leading edge to the trailing edge of the wing, and the relative wind, which is the direction of the airflow relative to the aircraft. Understanding the angle of attack is crucial for pilots because it directly affects lift and the performance of the aircraft. As the angle of attack increases, lift generally increases up to a certain point, beyond which the wing may stall if the angle becomes too steep. This concept is fundamental to understanding how aircraft generate lift and the principles of flight.

The other choices involve aspects of aircraft positioning or control surfaces that do not accurately convey the definition of the angle of attack. They address different concepts, such as the aircraft's orientation to the horizon or the position of control surfaces, but they do not encapsulate the definition that is critical for flight dynamics and safety.