Plain English Meaning
If you know how far you have flown over the ground and how long it took, you can find your speed over the ground by dividing the distance by the time.
Full Definition
A formula used in dead reckoning navigation to calculate groundspeed (GS), where groundspeed equals distance flown (D) divided by the time it took to fly that distance (T). Distance is typically expressed in nautical miles and time in hours, giving groundspeed in knots.
Context Anchor
Seen in flight planning and navigation calculations when estimating travel time, arrival time, and fuel needs.
Derivation
GS stands for groundspeed -- the aircraft's actual speed across the ground, as opposed to airspeed (speed through the ). The formula itself is the speed = distance ÷ time relationship from , applied to navigation.