International customary law

International customary law is like a rule that people around the world follow without anybody writing it down like we do with our school rules. It's like when your mom tells you not to hit your brother or sister because it's the right thing to do, and you know not to do it even if there isn't a written rule about it.

Now, imagine there are many countries in the world, and they all have different rules and laws. But there are some things that all these countries agree on, even if they don't write them down in a book. These are the things that make up international customary law.

For example, most countries agree that killing other people without a good reason is wrong. This is something that all countries try to prevent and punish. Even though there isn't a written rule that says it's wrong to kill, all the countries know it's not acceptable.

International customary law helps countries work together and understand each other even if they have different laws. It's like a secret agreement that everybody knows and follows, even if we don't say it out loud.