Book excerpt: Of all the anomalous phenomenon reported, ghost sightings are by far the most common. The words "ghost" and "spirit" are used interchangeably in American English but in other cultures the lingering souls of the departed are not to be confused with ancestral spirits, demonic spirits, numens or poltergeists. This encyclopedia lists hundreds of entities of the spirit realm--from aatxe to zuzeca--from world mythology and folklore.