Final answer:
When a person is irreversibly unconscious, it is known as brain death. This means there is no hope of regaining consciousness even with medical treatment. Terri Schiavo is an example of someone in a vegetative state due to brain death.
Step-by-step explanation:
When a person is irreversibly unconscious with no hope of regaining consciousness even with medical treatment, this condition is known as brain death. Brain death is the complete and irreversible loss of brain function, including activity in the cerebral cortex which is responsible for consciousness and higher cognitive functions. While brain death is irreversible, the brainstem may still remain intact, allowing the person to have basic bodily functions like breathing and reflex movements.
An example of brain death is the case of Terri Schiavo, who went into cardiac arrest and suffered severe brain damage as a result. She was in a vegetative state and required a feeding tube to stay alive, but her brain activity was completely lost.