Brain death is a medical condition where a person has permanently lost all brain function, including the brainstem, which controls basic life-sustaining functions like breathing and heartbeat. This condition is diagnosed through a series of tests that confirm the absence of brain activity, and it is considered legally and clinically equivalent to death. In cases of brain death, the body may still be on life support, which can maintain circulation and breathing artificially. However, without brain function, the individual cannot recover or regain consciousness. This distinction is crucial for organ donation and end-of-life decisions.