It's basically understanding where you are in the air. It doesn't matter what "sport" you're doing, it could be on skis, on a trampoline, a diving board, whatever you are in the air during. It also involves all axises of the trick, so flip, spin, or off axis. Finally, the more flips/spins you're doing, the more air awareness required. getting your body to do one flip can be hard, getting your body used to that one flip and then telling it to do more is even harder. This is why tricks like Jesper's switch triple front flip are so impressive, they require an incredible amount of air awareness (plus that trick is supremely blind - so you rely only on your air awareness to know what's up and what's down).