Ground speed is the horizontal speed of an aircraft relative to the ground. An aircraft heading vertically would have a ground speed of zero. Information displayed to passengers through the entertainment system often gives the aircraft's ground speed rather than its airspeed.
Ground speed can be determined by the vector sum of the aircraft's true airspeed and the current wind speed and direction; a headwind subtracts from the ground speed, while a tailwind adds to it. Winds at other angles relative to the aircraft's heading will have not only a headwind/tailwind component, but also a crosswind component.
An airspeed indicator indicates the aircraft's speed relative to the air mass. The air mass may be moving over the ground due to wind, and, therefore, some additional means to provide position over the ground is required. This might be through navigation using landmarks, radio-navigation, an inertial-nav-system, or GPS (occasionally called gnss instead). When more advanced technology is unavailable, an E6B flight computer may be used to calculate groundspeed.
Ground speed is quite different from airspeed. When an aircraft is airborne, the ground speed does not determine when the aircraft will stall, and it doesn't influence aircraft-performance figures, such as rate of climb.