When people go to court, there are rules about what information they have to share with each other before they start the case. This is called "discovery."
Sometimes, the people who are in trouble with the law don't want to share all the information they have because they're worried it will make them look even worse. But, there's a very important rule that says they have to share anything that could help the other side. This is called "Brady disclosure."
It's like if you're playing with a friend and you have a really cool toy that they've never seen before. If your friend asks about the toy, it wouldn't be nice to keep it a secret because they might enjoy playing with it too. In the same way, hiding evidence that could help the other side isn't fair.
So, Brady disclosure makes sure that everyone has the information they need to make the best decisions and have a fair trial.