The most prevalent type of haunting, by far, is referred to as a residual haunting. In this type of haunting the ghostly energy goes through a cycle of actions over and over again. It's like a video clip that repeats itself in a loop. Oftentimes this plays out at a specific time as though it were following a schedule. Most commonly the scene played out will be that of a tragic event, such as a death. This type of haunting is more like a psychic impression of energy than an actual haunting by a presence or entity. Many true stories seem to describe this type of occurrence.
I have considered this, have written about it, and have not ruled it out; but I have not had it proven to me as factual, either.
I say this, because I also have another theory that could explain what many call a residual haunting:
What if the person who never communicates with the physical world, keeps doing the same action over and over, is effectively trapped in a state of mind (call it "hell") that is reliving a certain event for some purpose (be it protective, trauma, etc). That person (ghost) would need rescued from their self-created prison and helped to move along on the life-journey. Just a theory...
This is strange that Nitewing would say this, reason being is that we as ghosthunters have to keep an open mind. that is like my demon expert I have in my group. She feel that anything walking the earth is a demon. there is no such thing as a human haunt or the residual haunt. this is something I can not quite grab at yet.
I am thinking of starting a free banner exchange for anyone with a paranormal website. If you think this is a good idea then let me know. If there is enough interest I'd start it up.