During the season you’ll read plenty here at PBT (or from other writers) talking about it, you hear analysts mention it on broadcasts all the time:
Along with “floppy” and a few others it is one of the NBA’s standard sets that gets run by almost every team at points in a game. In a good video for a Friday night learning session, Coach Nick of BBallBreakdown walks you through the basics of horns and how a few teams work out of it (such as the Warriors with the elevator screen they run for Stephen Curry).
Watch this and come the season you will start to recognize this action all the time. Then when you’re watching a Warriors game at a bar you can yell out “horns” when they start the play… then the cute girl next to you gives you an odd look and moves a few seats down. So maybe don’t yell it out. But you’ll recognize it at least.