Ground speed is the horizontal component of the velocity of an aircraft relative to the Earth’s surface, also referred to as "speed over the ground".
[1] It is vital for accurate navigation that the pilot has an estimate of the ground speed that will be achieved during each leg of a flight.
Theoretically, an aircraft diving vertically and unaffected by wind would have a ground speed of zero.
When more advanced technology is unavailable, an E6B flight computer may be used to calculate ground speed.
When an aircraft is airborne, its ground speed is not related to the likelihood of a stall, and it doesn't influence the aircraft's performance, such as rate of climb.