A ghost, apparition, spirit, is the soul or energy, of a person who has passed and remains stuck between this plane of existence and the next. Researchers believe that these spirits do not know they are dead many times and haven't "passed over" yet.

They most likely have died under traumatic, unusual, or emotional incidents and may have some "unfinished business" to take care of before they pass over. Humans can detect ghosts in many ways, smell (odors/fragrances) sight (when a ghost materializes), sound (voices), touch (cold spots), and people who are clairvoyant or sensitive can sense their presence.  Ghosts are capable of interacting with the living, and animals can also take the same form.  There are countless accounts from people who have seen, felt and heard pets well after they have died. The animal usually behaves in ways that it did in life, carrying out its routines and habits such as jumping on a bed to cuddle with its owner.