The astral body is a person’s second body, which can be separated from the physical body. The astral body is the explanation of ghosts and out-of-body experiences.
It’s also said that when a person dies and is buried, they are only in a catatonic trance, explaining how people could survive long periods in the grave without food and air. While the physical body is in the grave, the astral body was projected to suck the blood or life-force from the living. When the body was dug up, it appeared as though it has recently gorged itself on blood.
The thought was that the blood or life that the astral body gorged itself on was passed to the organs and physical body immediately, and then the astral body would return to the physical one.
In order to stop the astral vampire, the physical body had to be burned and cremated to severe the ties between the two.