Okay, so let's pretend you're learning to ride a bike. You pedal really fast, and then you stop moving your feet. The bike will start to slow down, but you don't want to fall off, so you need to know when to start pedaling again before you come to a complete stop.
The backward differentiation formula is kind of like that. Let's say you have a bunch of numbers that are changing over time, like how fast a bike is going. If you know what those numbers are at a few different times (like how fast the bike is going every second for a few seconds), you can use the backward differentiation formula to figure out what the numbers were in the past (like how fast the bike was going a second ago).
It's called "backward" because you're figuring out what happened in the past, and "differentiation" because you're figuring out how much things changed. Basically, you use the formula to figure out how fast things were changing in the past, based on how fast they're changing now.
It's like if you're on the bike, and you know you're slowing down a certain amount every second, you can use that to figure out how fast you were going a second ago. And if you know how fast you were going a second ago, you can use that to figure out how fast you were going two seconds ago, and so on.
The backward differentiation formula is used a lot in math and science to help figure out things like how objects are moving or how things change over time. It's like being a detective and using clues to solve a puzzle!