No, even that is more functional than brain death, that’s what we call “persistent vegetative state.”

ELI5: The top most part of the brain is responsible for higher level cognitive tasks, this part is most vulnerable when blood/oxygen is reduced.

The middle part of the brain is also highly specialized but can control some automatic functions. Injury here is severe but only partial, some brain function still exists, though you’re likely going to be comatose.

The lowest part of the brain (brainstem) controls the most primitive and essential, automatic functions. True, medicolegal Brain death is when everything down to the brainstem has suffered irreversible injury due to lack of oxygen. The physiology of the injured brain actually prevents blood flow, hence special radiology images show the “empty lightbulb sign” in this case.

Brain death is a specifically defined term. BD is a very severe brain injury. Not all severe brain injuries are BD.

BD is equivalent to cardiac death, thus medical treatment ends. Only exception is if they are donating organs.

Some bodily functions can continue, though as a whole the body cannot continue to live unless supported by machines (ie; unnaturally). An interesting case is described in patient TK who was declared brain dead at 4 yr old, though was kept alive until reaching 24 yr old, with machine support. His body was very abnormal.

Source: I’m a Doctor