Death is the end of life. Whether it’s only an instant or it takes years, death is always permanent, no matter what vampire movies try to tell you.
Death has many meanings and uses, but it always means the end of something. It can be a single moment like the death of a fish eaten by an alligator, a slow process like the death of cassette tapes as compact discs became popular, or an ongoing state like the death of an ancient language. Death isn’t always bad: the death of a human is depressing, but the death of a vegetable is dinner.