What is 'brain death' and how does it factor into organ donation?

What it is: Under Canadian guidelines, it is defined as the irreversible end of all brain activity due to permanent loss of blood flow and oxygen to the brain.
What it is not: Brain death, or neurological determination of death, is not the same a vegetative state or coma, in which patients continue to have brain activity.
Where it came from: It was defined by an ad-hoc committee at Harvard University, which characterized it as: a non-functioning brain; total unawareness to external, or painful s