Yes, definitions are arbitrary but that is the definition of space.

What does "ISS" stand for again? I forgot.

The Karman Line's lowest theoretical point is still substantially higher up than commercial airplanes and its highest is substantially lower than the ISS. Most nations agree on it as the boundary for the purposes of law and regulation. Commercial airplanes fly about half as high as the line, while spacecraft orbit at four times its altitude or more.

It may be scientifically arbitrary, but it's got a lot going for it as a rough approximation.

Thank you for the accents

My favorite fact is that earth's atmosphere extends 95,000 miles / 150,000 km beyond the moon.

Extremely pedantically, sure. But under that level of pedantry, the whole metric falls apart anyway because there's surely never or rarely been a point in recorded human history where someone hasn't jumped/fallen/not been physically touching the ground themselves (let alone this having been measurable). What about "touching"; your feet are just repelling the ground via electromagnetism.

It's really obvious what the metric is, and trying to pedant-proof it isn't worth bloating it into a mouthful. We can just recognize what it obviously means, say "oh, neat", and move on with our day.

I guess you could count the atmosphere as part of earth, then things over 100km are in little enough of the atmosphere that it's not really 'touching' it the same way. (For example not generating significant lift)

The word I used was "supported by" the ISS does not have wings and does not have a buoyancy system, they are falling

The plane is riding on wings you can tell it is not falling because you feel your full weight when riding one