Millwall brick

Okay kiddo, so a millwall brick isn't really a brick like the ones you see used to build buildings. It's actually just a piece of paper that's been folded up tightly to make it hard and compact.

The reason it's called a millwall brick is because it was often used as a weapon at soccer matches by fans of the Millwall football club in England. They would fold up pieces of newspaper or magazine pages into a small, hard object that they could use to defend themselves or attack others if needed.

So, it's not a real weapon and you should never use one to hurt anyone. It's just something that some people in England used to carry around as a way to protect themselves at soccer matches.