Death is the permanent cessation of all biological functions that sustain a living organism, marked by the irreversible stoppage of heartbeat (cardiac arrest), breathing (respiratory arrest), and brain activity (brain death). Legally and medically, it is confirmed when there is no spontaneous heartbeat or respiration and no brain stem reflexes (including pupils fixed and unresponsive to light, no corneal reflex, no spontaneous breathing when ventilator support is removed in brain death testing), or in some cases, irreversible cessation of circulatory and respiratory function. It represents the end of life processes, after which consciousness, sensation, and bodily functions cease entirely. Causes range from natural processes (aging-related organ failure, terminal illness) to acute events (trauma, cardiac arrest, stroke, severe infection/sepsis, poisoning, or violence), with the moment of death often preceded by agonal breathing, loss of consciousness, mottled skin, cooling of the body, and eventual rigor mortis, livor mortis, and decomposition if not preserved. In philosophical, cultural, or spiritual contexts, death is viewed variably as the end of existence, a transition to an afterlife, reincarnation, or nothingness, but biologically it is the definitive end of an individual’s life cycle.