The meaning of "death" has changed over time. "Whaaaa?" you say. Yeah, it seems weird to us too. But considering society's ability to keep people awake and breathing long past the point they would've been able to keep going even 50 years ago, it makes sense.

As a starting point, let's begin with the first definition as it first appeared in the good ol' Encyclopedia Britannica in 1768: "DEATH is generally considered as the separation of the soul and body; in which sense it stands opposed to life, which consists in the union thereof."

Pretty simple, right? Well, not really. Here are a few examples of just how difficult defining death can be:

Scientific Meaning
The medical community basically defines death as a series of functions or characteristics that a living person has and a dead person lacks. Specifically they're concerned with spontaneous respiratory function (can you breathe?), cerebral function (is your brain still working?), and spontaneous circulatory function (is your heart pumping?).

In case you're wondering, the "spontaneous" part wasn't always included in the scientific definition. Today, however, it's an important component since machines can keep a person's blood flowing and lungs breathing.

Legal Meaning
Yes, teams of people have actually sat around to come up with criteria for the legal determination of death. The Uniform Determination of Death Act (written by the National Conference of Commissioners on Uniform State Laws in 1980) is one example of such a meeting, and its guidelines remain important to this day.

According to the UDDA a person must have either an, "irreversible cessation of circulatory and respiratory functions OR irreversible cessation of all functions of the entire brain, including the brain stem," in order to be declared dead.

So, if your brain stops working or your heart and lungs go kaput, according to your lawyer, you're dead. Based on several laws enacted by various states, the criteria outlined in the UDDA along with medical advancements have been the cause of much controversy regarding the definition of death. According to the UDDA, a person who is brain dead is considered dead even though his or her other organs are keeping him or her alive because, essentially, he or she is unable to have a "life."

Spiritual & Cultural
The significance of death changes depending on one's culture or spiritual preference. For many religions--Christianity or Judaism for instance--death is defined as the separation of the physical (body) and spiritual (soul). But instead of being seen as an unequivocal loss, death is the means by which the soul returns to God. It could also mean eternal damnation, a much less joyous event.

Death means something completely different on the Indian continent, where the majority of people believe in reincarnation. Death is simply the continuation of the cycle of life and rebirth, by which the soul is recycled into another physical body. This cycle continues until the soul reaches some goal and enters into a state of non-being. (See Beliefs & Death Rituals for more info)