Brain death means that the brain has stopped working. Brain death is permanent, and cannot be cured or reversed. No treatment can help. When a person is brain dead, there is no activity in any part of their brain. Every part of the brain is dead; no oxygen flows to the brain, and there is no electrical activity in any part of the brain.
The brain controls everything we need to do to stay alive. For example, it controls breathing, body temperature, heart rate, and many other important things. When a person is brain dead, their brain cannot control any of these things. A brain-dead person cannot breathe on their own. They will never be able to wake up or be aware of what is going on around them.
Sometimes, brain-dead people are kept alive with special machines and medications. For example, doctors can put a tube down a person's throat and use a machine called a ventilator to pump oxygen into their lungs. While these machines can keep the person's other organs alive for a while, they cannot help the brain get better. Eventually, the person's other organs will stop working too.