Airplay is how much a particular song is played on the radio — the time it is actually “on the air.” If a song gets a lot of airplay, many stations are playing it, so more people hear it. DJs, managers, and charts care about this; it is a music-business word more than a family word. People also stretch it a little to television music channels, but the home meaning is radio. Though actually, air here is not the sky and not the stuff we breathe. It is the old idea of a programme going out on radio waves. Plays on a phone app are usually just called plays or streams, not airplay. You would not use airplay for children playing outside, and you would not use it for a band playing on a stage unless that show is being broadcast.