Defining life to define death
One of the challenges in defining death is in distinguishing it from life. As a point in time, death seems to refer to the moment when life ends. Determining when death has occurred is difficult, as cessation of life functions is often not simultaneous across organ systems.[20] Such determination, therefore, requires drawing precise conceptual boundaries between life and death. This is difficult due to there being little consensus on how to define life.
many religious traditions, including Abrahamic and Dharmic traditions, hold that death does not (or may not) entail the end of consciousness. In certain cultures, death is more of a process than a single event. It implies a slow shift from one spiritual state to another
death occurs when a living entity experiences irreversible cessation of all functioning.[24] As it pertains to human life, death is an irreversible process where someone loses their existence as a person.
type of death where circulatory and respiratory arrest happens is known as the circulatory definition of death (CDD)
https://en.wikipedia.org/wiki/Brain_death
brain death" or "biological death"
people are considered dead when the electrical activity in their brain ceases
It is presumed that an end of electrical activity indicates the end of consciousness.
Suspension of consciousness must be permanent and not transient, as occurs during certain sleep stages, and especially a coma.
brain death" cannot be equated with one in a vegetative state or coma, in that the former situation describes a state that is beyond recovery.
In the case of sleep, electroencephalograms (EEGs) are used to tell the difference
hospitals have protocols for determining brain death involving EEGs at widely separated intervals under defined conditions
the criterion for death may be the permanent and irreversible loss of cognitive function, as evidenced by the death of the cerebral cortex. All hope of recovering human thought and personality is then gone, given current and foreseeable medical technology.
Even by whole-brain criteria, the determination of brain death can be complicated.
Law
At present, in most places, the more conservative definition of death (irreversible cessation of electrical activity in the whole brain, as opposed to just in the neo-cortex) has been adopted
https://en.wikipedia.org/wiki/Unifor
m_Determination_Of_Death_Act