3.  1) Earthbound spirits "haunting" a particular location.

2) A psychic "recording" of emotional energy released during traumatic experiences of suicide, murder, accidental death and painful dying. As a psychic recording, it can be reproduced and experienced by psychically sensitive people and almost always at night when nothing competes with the reception. These experiences are often accompanied by fear which then reinforces the initial energy. Like other kinds of recording, the original energy can often be released or erased by "overwriting" with other strong releases of emotion such as a ritual exorcism, happy children, shamanic practices, and even loud music.

Suggested Reading:

Danelek: The Case for Ghosts, An Objective Look at the Paranormal

Wilder: House of Spirits and Whispers, The True Story of a Haunted House