Ghosts are the essence of someone who has died, and are seen in cold, misty apparitions. They cannot do much to interact with the living or with physical objects, aside from pushing their energy at things. They cannot speak, either, and often haunt places where they lived frequently or where they died.
Spirits are the souls of those who have died, but have come to the living realm to interact with the living. They are often seen as translucent and their bodies have no heat, but they are not as cold and misty as ghosts. They can speak, but their voices are often noted to be softer than in life. They can also touch and interact with the living and physical objects.
While ghosts exist of their own accord, they can be convinced to pass on to the Spirit Realm by Asirim and priests. Spirits cannot enter or leave the living realm without an Asir opening a door for them.