There are many different kinds of hauntings, and even more expressions to describe them. However, there are two primary categories of hauntings: Active or 'intelligent' hauntings, involving the presence of a sentient spirit or ghost;
and
Residual energy imprint hauntings--often called 'residual energy hauntings' or 'imprints'--which are the products of an emotional incident, often a violent event.
Just like an iron remains hot long after it's turned off, strong energy seems to be stored in physical surroundings.
When someone witnesses this kind of haunting and is startled or frightened by it, that energy may refuel the setting so that the manifestations and/or impressions continue.
This may also account for the phenomena of haunted objects.
What others say about residual energy hauntings
Ghost hunters may disagree about the frequency and importance of residual energy hauntings. We may use different terms for it. But, we usually agree about what it is:
In Ghosts, Spirits and Hauntings, author Patricia Telesco uses the term 'memory imprint' and describes it as, 'An energy remnant that leaves a mark on a room or region.'
Although it is unlikely, in The Field Guide to Ghosts and Other Apparitions, authors Evans and Huyghe call it a 'memory trace' and relate it to a psychic 'tape recording of a voice' that some witnesses can perceive.
In The Complete Idiot's Guide to Ghosts & Hauntings, Tom Ogden describes a 'residual haunting... a sudden displacement in time during which you see into or experience the past'.
Cassandra Eason, in Ghost Encounters, refers to imprints in terms of a 'worn-out reel of film constantly replaying in an empty cinema' and dismisses them as hauntings.