Simply we can describe them as some energy forms which are not bound by any physical bodies.

Let us read about a few kinds of ghosts.

Ghosts

A ghost can be described as a spirit or apparition and is known to be the power, person or qualities of a person who has died and somehow (No proven theory) got trapped between the plane of survival and the dead. Almost many researchers think that these spirits do not know they are dead. But over and over again they have died under highly emotional circumstances. They can be apparent a number of ways by the living: through view, sound, fragrance, touch and even they can just be sensed at times.

Haunting

Foot paths of past events in the environment like house, building etc is termed as haunting.  These foot paths occur in loops like a video tape. How does it happen? And the thought will be, it’s the presence of certain people who trigger these foot paths to play again and again. By this we cannot term them as ghosts and they cannot interact with the living. There are no scientific explanations for these foot paths and triggers but they are associated with an emotional event.

Poltergeist

Poltergeist is know as noisy spirit and falls under a German word. Intense investigations have told us that poltergeist have nothing to do with ghosts or spirits. This activity occurs with individuals and the cause is seemed to be with the subconscious mind of that particular individual who is emotional or with physical stress or psychological affected. There are no scientific explanations for the results and the results include physical movement of objects, effects on electrical equipments, even rapping on floors and walls.

Orbs

Orbs are ghosts in the shape of balls of light. They are life forms that travel in groups and are supposed to be the human soul of those that once inhabited a physical body. It is believed that these spirits that have stayed behind because of their bond to their life. Because of this obsession they tend to become similar to psychotic human beings. It should be said that the majority of us when we die proceed gladly and willingly to the next level of existence. But, a select few elect to stay behind because of their refusal to move on. Apparently the longer they stay behind, the harder it is to find their way to the next level, which again, is the spirit world.

Ghostly orbs are the most photographed anomalies caught on film and are very photogenic. They could be transparent or display themselves in a bright form. It is theorized that ghosts prefer the form of an Orb because it takes less energy. The consent is that small orbs take up the least amount of energy and apparitions and other fuller shapes take up the most. In the colder times of the year, ghosts take on shapes other than orbs. That's when there is more static energy in the atmosphere. It is also believed that they are able to draw on our own energy if needed

Other than the above mentioned there are several other kind of ghosts, but be assured that 99% of these ghosts are harmless. Just leave them the way they are and don’t try to disturb them – remember they were once living.