CBRN defense is like playing dress-up, but you wear special clothes and gear to protect yourself from bad things that you can't see or smell.
CBRN stands for Chemical, Biological, Radiological, and Nuclear. These are things that can hurt people or make them sick really fast.
The clothes you wear have a special kind of fabric that stops bad stuff from getting on your skin. You might wear a big suit with a hood that covers your whole head. You also wear special gloves and boots that cover your hands and feet.
But just wearing clothes isn't enough. You also need special gear to help you breathe. There are big masks with filters that clean the air so you don't breathe in any bad stuff. They can be a bit scary because they cover your whole face, but they keep you safe.
CBRN defense is very important for people who need to go into dangerous areas. Soldiers might wear this gear when they go to war, or firefighters might wear it when there's a fire that releases harmful chemicals. By wearing CBRN gear, they can do their jobs and help people without getting hurt themselves.