Death is the permanent termination of the biological functions that sustain a living
Life is a characteristic that distinguishes objects that have signaling and self-sustaining processes from those that do not, either because such functions have ceased , or else because they lack such functions and are classified as inanimate...

In biology, an organism is any contiguous living system . In at least some form, all organisms are capable of response to stimuli, reproduction, growth and development, and maintenance of homoeostasis as a stable whole.An organism may either be unicellular or, as in the case of humans, comprise...

. Phenomena which commonly bring about death include old age, predation
In ecology, predation describes a biological interaction where a predator feeds on its prey . Predators may or may not kill their prey prior to feeding on them, but the act of predation always results in the death of its prey and the eventual absorption of the prey's tissue through consumption...

, malnutrition
Malnutrition is the condition that results from taking an unbalanced diet in which certain nutrients are lacking, in excess , or in the wrong proportions....

, disease
A disease is an abnormal condition affecting the body of an organism. It is often construed to be a medical condition associated with specific symptoms and signs. It may be caused by external factors, such as infectious disease, or it may be caused by internal dysfunctions, such as autoimmune...

, and accident
An accident or mishap is an unforeseen and unplanned event or circumstance, often with lack of intention or necessity. It implies a generally negative outcome which may have been avoided or prevented had circumstances leading up to the accident been recognized, and acted upon, prior to its...

s or trauma resulting in terminal injury.

The nature of death has been for millennia a central concern of the world's religious traditions and of philosophical enquiry
Philosophy is the study of general and fundamental problems, such as those connected with existence, knowledge, values, reason, mind, and language. Philosophy is distinguished from other ways of addressing such problems by its critical, generally systematic approach and its reliance on rational...

, and belief in some kind of afterlife
The afterlife is the belief that a part of, or essence of, or soul of an individual, which carries with it and confers personal identity, survives the death of the body of this world and this lifetime, by natural or supernatural means, in contrast to the belief in eternal...

 or rebirth
Reincarnation best describes the concept where the soul or spirit, after the death of the body, is believed to return to live in a new human body, or, in some traditions, either as a human being, animal or plant...

 has been a central aspect of religious faith.
The word death comes from Old English deað, which in turn comes from Proto-Germanic *dauþaz (reconstructed by etymological analysis).

Men fear death, as children fear to go in the dark; and as that natural fear in children is increased with tales, so is the other.

Francis Bacon, Essays, 2, ‘Of Death’

We all labour against our own cure; for death is the cure of all disease.

Thomas Browne, Religio Medici, II. 9.

What argufies pride and ambition? Soon or late death will take us in tow: Each bullet has got its commission, And when our time's come we must go.

Charles Dibdin, Each Bullet has its Commission

Verse, Fame and beauty are intense indeed, But Death intenser – Death is life's high mead.

John Keats, Sonnet: Why did I laugh to-night?

Death opens unknown doors. It is most grand to die.

John Masefield, Pompey the Great, i.

Death hath a thousand doors to let out life: I shall find one.

Philip Massinger, A Very Woman, V. iv.

Death did not come to my mother Like an old friend. She was a mother, and she must Conceive him. Up and down the bed she fought crying Help me, but death Was a slow child Heavy.

Josephine Miles, "Conception" (1974) st. 1–2; Collected Poems, University of Illinois Press, 1983