Define “airspeed.”

Airspeed is defined as the speed of an aircraft relative to the air through which it is flying. This measurement is crucial for understanding an aircraft's performance characteristics, as it directly impacts lift, stall speed, and control effectiveness. Airspeed is typically indicated on the aircraft's airspeed indicator and is vital for pilots to ensure safe and efficient flight operations.

Understanding airspeed in terms of its relationship to the surrounding air rather than the ground is essential because it determines how well the aircraft can interact with the air to generate lift and maneuver. For instance, the stall speed of an aircraft is defined in terms of airspeed, meaning that the aircraft must maintain a specific speed relative to the air to avoid stalling.

While other terms like ground speed, which refers to the speed of the aircraft relative to the Earth’s surface, are important in navigation, they do not affect aerodynamic performance directly. Therefore, the focus on the aircraft's speed relative to the air is what establishes airspeed as a critical factor in flying safety and aircraft performance.