Short answers, pulled from the story.
Death is the end of life, the irreversible cessation of the biological functions that sustain a living organism. The study of death is known as thanatology. Identifying the exact moment of death is difficult because life functions do not cease simultaneously across all organ systems.
As of the early 21st century, 56 million people die per year. As of 2022, an estimated total of almost 110 billion humans have died, roughly 94% of all humans who have ever lived. About 150,000 people die around the world each day.
Brain death is when the electrical activity in a person's brain ceases, and it is sometimes used as a legal definition of death. It is controversial because patients diagnosed as brain dead and kept on mechanical ventilation can still sustain circulation, control temperature, heal wounds, fight infections, and even gestate fetuses. Definitions also differ between whole-brain, neocortical, and brainstem criteria.
After death the body passes through pallor mortis, a paleness occurring 15 to 120 minutes after death, then livor mortis, algor mortis, and rigor mortis. These are followed by putrefaction, decomposition, skeletonization, and eventually fossilization. An autopsy, performed by a pathologist, examines the corpse to determine the cause and manner of death.
The leading cause of death in the developed world is biological aging, known as senescence, which leads to aging-associated diseases. Of the roughly 150,000 people who die each day, about two-thirds die of age-related causes, and in industrialized nations the proportion approaches 90%. In developing countries, infectious disease is the leading cause.
Cryonics is the low-temperature preservation of animals, including humans, who cannot be sustained by contemporary medicine, in the hope that healing and resuscitation may be possible in the future. The word comes from the Greek kryos, meaning icy cold. Cryopreservation of people and large animals is not reversible with current technology, and medical science and cryobiologists generally regard it with skepticism.