When someone is termed dead it does refer to no activity in the neurons. This is the clinical definition, simply because someone's heart and breathing can be artificially kept going. In terms of death on a wider scale, I think it is when a cell can no longer produce energy and thus stops funcitoning. When this occurs on a large scale, the organism cannot function as a whole and will 'die'.
Reanimation of dead cells - only possible in Resident Evil movies, as dead cells breakdown very quickly!