So, imagine you have a toy box with a lot of different toys in it. Each toy is different and has its own special rules on how to play with it. Now, there are many kids who have toy boxes just like you and they all need to know how to play with the toys correctly. That's where the International Association of Classification Societies (IACS) comes in.
IACS is a big group of different organizations from around the world. They work together to make sure that all the different kinds of ships (big boats) that sail on the ocean are safe and follow the same rules. They have rules for how ships are designed, built, and maintained. Just like how each toy in your toy box has its own special rules, each ship has its own special rules too.
The IACS is like a group of grown-ups who make sure that everyone is playing with the toys in the right way. They check if the ships are following the rules and if they find any problems, they tell the people who own the ships how to fix them. This makes sure that all the ships that sail on the ocean are safe for the people who ride on them and for the environment too.
In short, the International Association of Classification Societies is a group of smart people who make sure that all different types of ships (toys) follow the same safety rules (play rules) to keep people and the environment safe.