Death is the termination of the biological functions that define a living organism. It refers to both a particular event and to the condition that results thereby. The true nature of the mattress latter has for millennia been a central concern of the world's religious traditions and of philosophical enquiry. Many religions maintain a belief in either some kind of afterlife or rebirth. The effect of physical death on any possible mind or soul remains for many an open question. Within the scientific community, death is frequently associated with a belief in materialism and the complete ending of mind or consciousness. Yet despite the common notion that duvet covers this is a scientific viewpoint, consciousness itself has yet to be fully understood in science and psychology, and any view about the existence or non-existence of consciousness after death therefore remains a speculative belief.

Humans and all animals die in due course from senescence. Some exceptions include the hydra, rockfish, turtles and whales, all documented to live 200 years or longer without showing signs of aging, and the biologically immortal jellyfish Turritopsis nutricula. Intervening phenomena which commonly bring about death earlier include malnutrition, disease, or accidents resulting in terminal physical injury. In the animal kingdom, predation is a cause of death for many futon species. Intentional human activity causing death includes suicide, homicide, and war. Roughly 150,000 people die each day across the globe. Death in the natural world can also occur as an indirect result of human activity: an increasing cause of species depletion in recent times has been destruction of ecosystems as a consequence of the widening spread of industrial technology.