Apparitions – Parapsychological Definition:
Apparitions are usually visual but sometimes in other sense-modalities in which there appears to be present a person or animal (deceased or living) and even inanimate objects such as carriages and other things, who/which is in fact out of the sensory range of the experient; often associated with spontaneous extrasensory perception, for example, in connection with an agent who is dying or undergoing some other crisis (in which case, it is likely to be termed a “crisis apparition,” or in connection with haunting (in which case, it is likely to be referred to in non-technical contexts as a “ghost”).
An apparitional double or counterpart of a living person.
As popularly used, this term denotes only the apparition of a deceased person, and is not sufficiently precise for use in psychical research.
The more or less regular occurrence of paranormal phenomena associated with a particular locality (especially a building) and usually attributed to the activities of a discarnate entity; the phenomena may include apparitions, poltergeist disturbances, cold drafts, sounds of steps and voices, and various odors.
Ashby, R.H. (1972). Glossary of terms in The Guidebook for the Study of Psychical Research and Parapsychology (Rider)
Thalbourne, M. (2003). Glossary of Terms Used in Parapsychology (Puente Publications). Refer Parapsychological Association