What is a Ghost? (About.com) by SpookyLady InSanDiego

There are many thoughts out there on just what ghosts are. Here are some from About.com Paranormal Guide Stephen Weber:

A ghost could be…

A dead person. Famous parapsychologist Hans Holzer wrote, “A ghost is a human being who has passed out of the physical body, usually in a traumatic state and is not aware usually of his true condition. We are all spirits encased in a physical body. At the time of passing, our spirit body continues into the next dimension. A ghost, on the other hand, due to trauma, is stuck in our physical world and needs to be released to go on.”

A residual haunting or recording. “A traumatic moment in time leaves an indelible impression on the building or area,” says Strange Nation in What Is a Ghost?, “replaying itself for eternity. This could be anything from a ‘glimpse of the past’ – a recreation of some traumatic or emotion-laden event – to footsteps up and down a hallway.”

A messenger. “These spirits usually appear shortly after their deaths to people close to them,” Stephen writes. “They are aware of their deaths and can interact with the living. They most often bring messages of comfort to their loved ones, to say that they are well and happy, and not to grieve for them. These ghosts appear briefly and usually only once. It is as if they intentionally return with their messages for the express purpose of helping the living cope with their loss.”

A poltergeist. Poltergeist means “noisy ghost” in German. Poltergeists are typically associated with unexplainable noises, footsteps, music, moving objects, slamming doors, turning lights off and on, flushing toilets, throwing things or sometimes even interacting with the living in the forms of pulling hair, clothing or even hitting people. Others believe these instances are simply psychokinetic episodes caused by people under stress.

A projection. Some people believe ghosts are simply a product of our minds. “A grieving widow sees her dead husband because she needs to; she needs the comfort of knowing that he is alright and happy in the next world. Her mind produces the experience to help itself cope with the stress of the loss,” writes Stephen.