Spirits are the essence of a dead being. They leave their bodies after death. Once they have lost their reason to remain on the physical plane, depending on the deeds they've committed during their living years, they are either accepted to heaven or dragged to hell. The spirits of supernaturals usually linger longer and are more powerful. Spirits and Ghost Whispering is a Taboo among Supernaturals.
Not every living being can see ghosts, and usually, no ghost can make themselves visible unless they contain extremely powerful surge of energy that allow them to appear to humans. However, this occasion is highly rare and unlikely. There is one way to see spirits. A Ghost Whisperer.