Define 'airfoil' in aviation.

An airfoil is defined as a structure designed to obtain lift from the air. This concept is fundamental in aviation because airfoils are essential elements of aircraft wings and propellers, where their shape and design allow them to manipulate airflow effectively. When air flows over an airfoil, the contour and angle of the surface create differences in air pressure above and below the wing, resulting in lift, which is crucial for flight.

Understanding the role of an airfoil is key for pilots and those involved in aviation design, as it directly impacts an aircraft's performance characteristics such as lift, drag, and overall aerodynamic efficiency.