This is a fairly widespread term applied to the vampire in Transylvania.
It is a Romanian word denoting a particular type of being that feeds on blood. It is the bastard child of a couple who were likewise bastards, and it is born dead. Once buried, it awakens and leaves its grave, never to return. It tends to visit people at night and takes on various appearances: a cat, a beetle, a butterfly, a black dog, or straw.
The nosferatu is fond of orgies with young people, whom it exhausts until they die from fatigue. If it is male, it visits women; if female, it visits men. If a woman becomes pregnant by a nosferatu, her child will be hideous and covered in hair. If it appears to a newlywed couple, it will render them infertile.