Ground speed

Ground speed is how fast you are moving across the ground when you are traveling in an airplane or a car.
Imagine you are walking on a moving sidewalk at an airport. If you walk in the opposite direction of the moving sidewalk, you will feel like you are moving very slowly, even though you are walking at your normal speed. This is because the sidewalk is moving in the opposite direction and canceling out some of your speed.
The same thing happens with airplanes and cars. If they are traveling against the wind or uphill, they will have a slower ground speed even if they are flying or driving at their normal speed.
On the other hand, if an airplane or car is moving in the same direction as the wind or downhill, they will have a faster ground speed than their normal speed.
So ground speed is how fast you are actually moving across the ground, taking into account the effects of wind and terrain, and not just how fast you are traveling in the vehicle.