Hello little one! Split S is a very special move that airplanes do when they need to turn around super fast. It's like when you turn around really quick while playing tag!
So here's how it works: when an airplane needs to turn around, it first flies straight and level. Then, it goes up into the sky and does a big flip. This is called a half-loop. Then, when it's upside down, it points its nose down to the ground and pulls back on the controls. This makes it start flying the other way, but really fast!
Now, the reason it's called a "split" S is because when the airplane is flying upside down, it looks like the letter "S" split in half! Pretty cool huh?
Pilots need to be really skilled to do a split S, because it's a very fast and tricky maneuver. But when they need to turn around quickly, it's a great tool to have in their toolbelt!