There are many answers to that question.  Some would say a ghost is an overactive imagination, some would say a spirit or the soul of someone who has died, others would say they have no idea. 

  Our definition of a ghost is "trapped, contained, or concentrated energy with variance, from an unknown source that causes a number of disruptions and/or disturbances."  

 What happens when energy gets trapped? (And yes, it can be trapped, we do it all the time; windmills, solar panels, transformers) When energy is trapped it becomes concentrated, when concentrated it can become unstable and manifest as noises, movement, light and apparitions.  S.P.I.R.I.T may refer to a ghost as a haunting, spirit, entity, or energy force. We can determine the type of ghost by one of five haunting classifications:

Natural: A natural haunt is initially unexplained phenomenon that occurs and that upon investigation is found to be caused by natural occurrences. For example I was working at a department store and one of the lady's I worked with knew I did paranormal investigations and asked if I could help her. Well sure I said. She proceeded to tell me that her six year old daughter kept having night mares and she didn't wont to go to her bed, because this monster was going to get her. She said that was pretty normal most kids don't ever want to go to bed, But the thing that had her really concern was that when she made her daughter sleep in her room. She would wake up with scratches. What do you think could be the cause of the scratches, she asked. I told her that I could be one of two things. The first was it could just be your daughter is scratching her self while she's asleep and not realizing it, or it could be a demon scratching your daughter. I told her thou to make certain of what was going on to set up a IR camera and record every night when her daughter went to bed. Well about a week went by and she came to me with a big smile on her face. Thank you, thank you. For what?. I did what you told me to, and I finally found out that my daughter was turning over in her bed and there is a rough place on the side of the bunk bed and she was getting scratched from that. So when you go in to an investigation kinda have an open mind, even when you do get something on video or tape. See if you can recreate it, or if you have a doubt about don't even use that piece of evidence. You always need to try to rule out things. For example lights flickering that are caused by loose connection or faulty wiring, noises that are found to be caused by pipes, animals, tree limbs, etc., apparitions that are found to be caused by mirrors, lighting, and reflections, etc.

Residual: A residual haunt is the next most common type of haunt. These are the cases where the same apparition, noise, or occurrence happens in the same pattern, usually at the same time. It can be something that happens daily, monthly or once a year. It may not always occur at the same time, but it will always occur in the same manner. These haunts are best explained as an imprint made in time, like a recording. There is no Spirit actually present, only the energy of a past occurrence. There is rarely danger in this type of haunt. It's exactly like a video playback of a historic or tragic event. The event unfolds in front of you and there is no interaction between you and the ghosts. They seem to not notice you and go through the motions of the event that occurred in the past. This event has been imprinted on the area of building and is replayed back later when conditions are right. The ghosts that you see in this type are not earthbound spirits; they are just visual playbacks. Since everything is

made up of energy, the theory is that some of the energy from an event can be recorded by certain materials and played back when the atmosphere triggers it. Remember that video and audiotape is just oxidized (rust) film that enables the images and sounds to "stick" to it.

Intelligent: An intelligent haunt possesses a human personality and seems to have and to react to emotions. It will react to it's environment and seem to try to communicate with the living, sometimes by moving furniture, appearing, making sounds, etc. They can appear as a full apparition, mist, shadow, orb, plasma. They can appear or verbally communicate to a certain person or a group, or in photos and E.V.P.'s. Their emotions can range from contentment, hopelessness, loneliness, confusion, and anger. They can and will act out their emotions as well as react to the emotions of the living. It can be very unstable in dealing with this type of haunt. It is extremely important to keep your emotions in check while investigating. When investigating you may here voices, music, footsteps, etc. You may also smell odors which sources cannot be found (i.e. pipe tobacco when no one smokes). You may also see orbs, mists and other light effects. You may feel touches, cold spots, and other light physical contact.

Poltergeist: The poltergeist haunt can be very terrifying. Activity will include a combination of knocks, bangs, furniture and items moving or being thrown, voices and apparitions. Poltergeist activity seems to increase and gain strength over time and is often negative or angry. In most poltergeist haunting there is almost always a female teenager living in the home or a very high level of stress in the home. Poltergeist seems to be closely connected or affected by one person in particular in the home. Often poltergeist is a result of several spirits feeding off of negative energy in the home and pooling that energy together. A poltergeist may appear and disappear with out warning. Activity can occur for days and then stop suddenly and not happen again for moths or years. A poltergeist haunt closely resembles and could very well be an intelligent haunt with one exception; poltergeist is extremely more active than intelligent haunt and is centered on anger. Poltergeist activity could easily be mistaken for demonic haunt, however there are elements in a demonic haunt that are not found in the poltergeist haunt. The best way to deal with the poltergeist haunt is to find the root of the anger or the stress that it feeds on and try to eliminate it. Again, it is extremely important for you to keep your emotions in check and never deal with a poltergeist haunt in anger or in a negative way.

Demonic: The demonic haunt is rare and very easy to identify, if it's not hiding. Signs of a demonic haunt are a revolting stench of sulfur or rotting flesh, growling, howling, pushing, shoving, hitting, scratching, air will feel thick, noises in three's (this is the demon making fun of The Father, Son, and Holy Spirit), temperature extremely warm, phantom mania (where the person feels like some one is holding them down and no one is there) and black masses. A demon can take on any form, most commonly half man, half animal. In most cases, the demon will hide from an investigator, but if confronted by the investigator, will feel threatened and appear in a human form, often as a child. It is important to assess the activity before you arrived rather than during the investigation. The goals of demons is to break a persons free will in order to posses. This can take days, months or years; time is of the essence. They hate mankind and try to cause as much destruction and pain as possible. Demons cannot be destroyed and only be removed through exorcism and cleansing. If you find that the haunt is demonic, suggest they study up on spiritual warfare and the authority they have through Jesus Christ. Then refer them to some one who is qualified to do an exorcism and cleansing. (And don't hang around for it to play with you, leave as quickly as possible. Your presence can only worsen the situation.)

 Being able to analyze the situation and determine the type of haunting helps us to better understand and help with our clients needs.