Practically every culture on Earth since the dawn of time have had ghosts as part of their legends. Although not every culture has the same beliefs as to
exactly what a ghost it, most of them agree that ghosts have something to do with the spirit or energy of the dead. Some claim that ghosts are the spirits
that have not been able to find their way to the afterlife for one reason or another, that has either been left behind on Earth, or is making a visit to
Earth from the afterlife.
Most legends agree that ghosts are either completely invisible or very hard to see resembling mist or shadow. Considering that a ghosts have no physical
body, you wouldn't expect to see much. Visible or not, ghosts are said to have some control over the physical world, whether it be from merely allowing
people to feel their presence or by causing chaos by breaking things and making noises.
Most religions claim that a soul (if they believe in one) passes on either to an afterlife or into another body. Because of this, it is thought that most
ghosts are tormented in one way or another, whether it be from a violent death, fear of crossing into the afterlife, or inability to leave a particular
area. Because they are tormented, most ghosts are unstable and potentially dangerous. Some ghosts are thought to be evil and hurt or even kill people.
Some cultures believe that ghosts are capable of possessing a living person and forcing them to say and do things against their will. This of course is
also a very convenient way of explaining why you were doing something illegal. There are several documented cases of people claiming to be attacked,
violated, or plagued by ghosts.
Ghosts are often said to haunt or frequent a particular area. Specifically, they supposedly haunt houses,
graveyards, and areas of disaster.
Ghosts have become a large part of pop culture as well. The ghost story is a very common genre of of campfire tales, and are usually made to scare
or entertain children. Hollywood has, of course, gotten a hold of the ghost idea and made plenty of movies regarding ghosts.
Most skeptics claim that ghosts do not exist, and attribute the phenomena with wind, optical illusions, gullibility, and good old fashioned lying. Still,
most people believe in ghosts in one form or another, and many people claim to have witnessed a a ghost first hand.
Because Halloween is based on the spirits of the dead, ghosts are fully integrated into the holiday. Most cultures (Latin American, Japan, etc.) show
deep respect for the spirits of the dead, but in the United States ghosts are usually viewed as playful white bed sheets that are cute and silly.
wikipedia.org - Wikipedia's page on ghosts.