The page entry in The Book

Categories of Ghosts and Spirits
Influences: the mildest form of ghost. They manifest themselves in a
vague sort of "feeling" which adhere to places or accasionally
to objects. often unpleasantly, but in no more tangible form.
Poltergeists: the noisy ghosts. These manifest themselves by destructive
outbursts of energy, which cause physical results of various types,
usually involving the destruction of household objects or loud noises.
A poltergeist may manifest itself by moving or levitating objects.
Apparitions: the traditional ghosts, which are the shadowy figures
that appear and disappear. They are often associated with historical
locations. Some apparitions have been of the living, and others have
been animals and objects, for example ghost ships, phantom animals
or mysteriously appearing and disappearing objects.
Phantasms of the living: are apparitions of people who are still alive,
but who appear in one place while their physical body remains in
other. Such apparitions usually indicate: people who are on the
point of death, who manifest themselves to someone closely involved
with them; or are people who are conveying some message of urgency
(for example, the mother who appears to warn her child of danger) or
people who are asleep at the time and who project their astral bodies
accidently or intentionally.
Hauntings: when the characteristics of apparitions and poltergeists
are considered to result in psychic phenomena of an alarmingly high
rate or nature.