Okay kiddo, imagine you and your friends are playing a game where you trade toys with each other. You first trade your doll for your friend's truck, and then you trade the truck for your other friend's ball. But then one of your friends disappears with your doll, so you can't trade anymore.
Now, in the grown-up world of business, sometimes a business buys things from another business and then sells them to someone else for a higher price. This is called trading. But sometimes, one of the businesses doesn't pay the other business for what it bought, and then disappears with the money. This is called missing trader fraud.
It's like if you were all grown up and working at a store that sells toys, and your store buys some toys from another store that disappears without giving your store the toys or the money. Then the toys are missing, and the store lost money. That's not fair, right?
The grown-ups who work in businesses have to be careful to make sure they are trading with honest and trustworthy businesses so they don't fall victim to missing trader fraud.