ISO 13600 is a set of rules that tells people how to make sure things are safe when they get sent through the mail. You know how you might get a letter from your grandma or a present from your friend in the mail? Well, the people who make those things and the people who send them want to make sure they don't get damaged on the way to you.
So, ISO 13600 helps them do that by giving them guidelines to follow. They have to make sure the things they send are strong enough to handle being bumped around and that they won't break or spill their contents. They also have to make sure the packaging won't hurt anyone or the environment.
Think of it like when you're packing your backpack for a school trip. You want to make sure everything you put in there is safe and won't get ruined on the way. ISO 13600 is like a grown-up version of that!