मृत्यू म्हणजे जीवित प्राण्याच्या शरीरातील त्या सर्व जैविक क्रियांचा अंत ज्या त्याला जिवंत राहण्यास मदत करतात. मृत्यूनंतर शरीराचे कार्य थांबते व प्राणी निष्क्रिय होतो. मृत्यूनंतर शरीराचे हळूहळू विघटन होण्यास सुरुवात होते. जन्म झालेल्या प्रत्येक जीवाला मृत्यू अपरिहार्य आहे.

• परम सत्य मृत्यू*

Death is the irreversible cessation of all biological functions that sustain a living organism. The remains of a former organism normally begin to decompose shortly after death. Death eventually and inevitably occurs in all organisms. Some organisms, such as Turritopsis dohrnii, are biologically immortal, however they can still die from means other than aging. Death is generally applied to whole organisms; the equivalent for individual components of an organism, such as cells or tissues, is necrosis. Something that is not considered an organism, such as a virus, can be physically destroyed but is not said to die, as a virus is not considered alive in the first place.