Question about "grounded " on terrains

I'm aware of what each terrain does. I also understand what "grounded" means (flying types, balloons, levitate...)

My question is the following: the not-grounded pokemon that ignores the terrain, is it the target, or the user of the move?

For example, with psychic terrain active, my Sableye (grounded) would like to use Disable on a Charizard (not grounded). Would the terrain block my priority?
What if the Sableye has an Air Balloon and the target pokemon is grounded, like for example, a Sneasler?

Thank you!