The physical body in general, or the idea that it’s just a physical “shell” in which a person lives during the course of their life.
If the body is someone you know, perhaps you consider that person to be reaching the end of a phase before beginning a new one, or perhaps you’re afraid of that person dying or becoming less unavailable to you (or at least not available to you in same way as before).
See also: Dead Acquaintance; Ending; Dying; Death of a Loved One; Ghost; Coffin