This thread is fun!

Actually aircraft do experience ground effect. When an airplane (small, single engine general aviation aircraft here) gets within a wingspan of the ground the air under the wings is compressed. This thicker air provides more lift so instead of settling down onto the surface the airplane tends to float above the surface before landing. So flying within a wingspan of the ground is considered to be in ground effect.

Of course what is considered "ground effect" in automotive terms may be completely different in aviation terms.

Sonoronos, your explanations are good so could you please explain a little more what ground effect is for cars?