Death is the end of life; 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. As of the early 21st century, 56 million people die per year. The most common reason is aging, followed by cardiovascular disease, which is a disease that affects the heart or blood vessels. As of 2022, an estimated total of almost 110 billion humans have died, or roughly 94% of all humans to have ever lived. A substudy of gerontology known as biogerontology seeks to eliminate death by natural aging in humans, often through the application of natural processes found in certain organisms. However, as humans do not have the means to apply this to themselves, they have to use other ways to reach the maximum lifespan for a human, often through lifestyle changes, such as calorie reduction, dieting, and exercise. The idea of lifespan extension is considered and studied as a way for people to live longer. Determining when a person has definitively died has proven difficult. Initially, death was defined as occurring when breathing and the heartbeat ceased, a status still known as clinical death. However, the development of cardiopulmonary resuscitation (CPR) meant that such a state was no longer strictly irreversible. Brain death was then considered a more fitting option, but several definitions exist for this. Some people believe that all brain functions must cease. Others believe that even if the brainstem is still alive, the personality and identity are irretrievably lost, so therefore, the person should be considered entirely dead. Brain death is sometimes used as a legal definition of death. For all organisms with a brain, death can instead be focused on this organ. The cause of death is usually considered important and an autopsy can be done. There are many causes, from accidents to diseases. Many cultures and religions have a concept of an afterlife that may hold the idea of judgment of good and bad deeds in one's life. There are also different customs for honoring the body, such as a funeral, cremation, or sky burial. After a death, an obituary may be posted in a newspaper, and the "survived by" kin and friends usually go through the grieving process. Source: Wikipedia (en)