What does ground speed refer to in aviation?

Ground speed refers to the speed of an aircraft relative to the earth's surface. This measurement is crucial for navigation, flight planning, and understanding how long it will take an aircraft to reach its destination. Ground speed is influenced by both the aircraft's speed through the air and the effects of wind—tailwinds increase ground speed, while headwinds decrease it.

In contrast, the other definitions do not accurately capture what ground speed represents. The speed of an aircraft relative to the surrounding air pertains to airspeed, which is important for understanding the aircraft's performance in flight, especially concerning lift. The speed during landing or in a climb refers to specific phases of flight rather than the overall measure of ground speed.