How is "airspeed" defined in aviation terms?

Airspeed in aviation is defined as the speed of the aircraft relative to the surrounding air. This is a crucial measurement for pilots, as it directly affects the aircraft's performance and handling characteristics. Understanding airspeed is essential for determining lift, drag, and fuel efficiency during various flight phases, including takeoff, cruising, and landing.

Using the surrounding air as a reference is important because it accounts for wind effects, which can significantly impact an aircraft's actual speed over the ground. For instance, when an aircraft flies into a headwind, its ground speed may be lower than its airspeed, while with a tailwind, the opposite can be true.

In contrast, the other options focus on different types of speed measurements. The speed relative to the ground is referred to as groundspeed, which does not provide the necessary information about an aircraft's ability to produce lift. Specific references to speed during takeoff or an average speed over the entire flight are too narrow in scope and do not encompass the full concept of airspeed as it is understood in aviation.