Quoted from yancy:
Wow man, that's next level pedantic. How about this mind-twister: cable shows don't actually air, because they don't come over the air! But if I stream Netflix on my iPad, Stranger Things is airing.
"Who cares," you might say. And you'd be right.
Why, thank you for the compliment! That's right, cable network shows don't come to the end user over the air, either. But they are distributed to the cable providers via satellite, d'oh! But seriously, airing refers to broadcast RF transmission, not streaming to a tablet. You're not "on the air" when sending a Pinside post over WiFi...
It is a funny term, though, seeing as how the radiation of RF energy has nothing to do with the air itself! (Except perhaps for ionospheric skip propagation at lower frequencies than TV uses, but the air is awful thin way up there.)
Heh heh, someone literally "on the air" had better have some sort of aeronautical support, like a plane or a parachute!
To be honest, the term is gradually being generalized. Someone live streaming a podcast could say they were on the air and I wouldn't blink.