Ghosts have been reported by every human civilization throughout history.  They often come in the form of unseen presences, translucent apparitions, or even lifelike, full-bodied images of people or animals.  Many believe that they represent the persistence of some sort of personality after death, but other explanations include the possibility that they're the visual memory of an event imprinted on an area, or even a glimpse into another time or parallel universe; while skeptics dismiss glimpses of ghostly phenomena as hallucinations and wishful thinking.  They are most often associated with a location, but some individuals have claimed to have a ghost attach to them specifically, following them from place to place.  There are arguments for and against each explanation for ghosts and hauntings, and it's even possible that each theory has its own place in reality.  Whatever the case may be, to the people who have encountered them, ghosts seem as real as anyone, and many dedicated researchers continue to question the nature of their existence even into the 21st century.