There are various states of the body/brain to which the label 'death' can be applied. Here is a quick guide to it, as posted in the other thread where this subject has cropped up:
Here is a brief passage from it:
Historically, attempts to define the exact moment of death have been problematic. Death was once defined as the cessation of heartbeat (cardiac arrest) and of breathing, for example, but the development of CPR and early defibrillation posed a challenge: either the definition of death was incorrect, or techniques had been discovered that really allowed one to reverse death (because, in some cases, breathing and heartbeat can be restarted). Generally, the first option was chosen. (Today this definition of death is known as "clinical death".)
Today, where a definition of the moment of death is required, we usually turn to "brain death" or "biological death": people are considered dead when the electrical activity in their brain ceases (cf. persistent vegetative state). It is presumed that a stoppage of electrical activity indicates the end of consciousness.
As to whether people can be raised from the dead, it is reasonable to presume that if you use the cardiac death definition then yes, but not if you use the brain death definition which is irreversible.