A controlled burn is like a big campfire that adults make on purpose. They decide where and when to start the fire, and they watch it very closely to make sure it doesn't get too big.
They do this because sometimes there are leaves, plants, or dead trees on the ground that can catch on fire really easily. This is dangerous because it can spread quickly and hurt the animals that live around there.
So, the grown-ups start the fire in a safe way and keep a close eye on it. They make sure it doesn't get too big and that it only burns the things they want it to. This helps to keep the animals safe and also helps the plants grow better because the fire gets rid of the stuff that's in the way.
After the fire is done, they also make sure it's completely out so it doesn't start back up on its own. The grown-ups take care of everything and make sure everyone and everything is safe.