What does the term 'groundspeed' refer to?

Ground speed refers specifically to the speed at which an aircraft is traveling over the Earth's surface. It is measured in relation to the ground rather than the air, which distinguishes it from other speed measurements such as airspeed. Ground speed is vital for navigation and determining flight time, as it reflects how quickly the aircraft covers distance relative to the ground underneath, factoring in both the aircraft's velocity and the effect of wind.

The other terms listed present different concepts: the speed of an aircraft relative to the speed of sound pertains to Mach speed, which is essential for understanding an aircraft's performance in different flight regimes. The total speed, including wind impact, often refers to effective airspeed or groundspeed when both the aircraft’s speed and wind direction are considered. The takeoff speed is a specific speed needed for an aircraft to become airborne, which does not directly inform us about how fast the aircraft is moving in relation to the ground after it has taken off.