Spirits were disembodied essences of deceased beings.
- Willow: "But why is it here? Does it just want to scare people?"
- Giles: "It doesn't know exactly what it wants. That's the problem. Many times the spirit is plagued by all manner of worldly troubles. But, being dead, it has no way to make its peace. So it lashes out. Growing ever more confused, ever more angry."
- — Willow and Giles
A ghost is the spirit of a dead person, who can't find eternal peace and have to walk the earth, trying to find it. It has unresolved issues and one of the only way to get rid of a ghost is to solve the problems. One other way is Exorcism. They're recognized by their inability to physically touch living beings.
- Xander: "Oh, no, not cool. This was no wimpy chain-rattler. This was more like - 'I'm dead as hell and I'm not gonna take it anymore"
- Giles: "Exactly. Despite the Xander-speak, that's an accurate definition of a poltergeist."
- Xander: "I defined something? Accurately? Check me out. Guess I'm done with the book learning!"
- — Xander and Giles[src]
A variant of the standard ghost is the poltergeist or "noisy ghost". A poltergeist is a very violent ghost, who not only can wreak havoc, but also possess individuals and force them to repeat the act, which doomed it in the first place. They can either be ghosts of people that have passed or mere apparitions.
Spirits of the dead that come to be in order to seek bloody vengeance on their oppressors (or their decendents) after years of unrest. They can take corporeal form and can only be killed by their own weapons. An example of a Vengeance Spirit is Hus.
A being that wasn't the disembodied spirit of a deceased person, but instead born out of raw emotion and pent-up energy. These apparitions manifest as poltergeists that feed on physical energy and draw it from the living world. When that battery is drained, the living participants die. An example include the Lowell House poltergeists.
Corporeal beings resembling deceased humans at the point of death that were summoned and controlled by a talisman. Destroying the talisman destroys the spirits.
Physiology and powers
A ghost can only be visible to the human eye with ectoplasm. When Spike was rendered incorporeal following the Battle at the Hellmouth, Fred's scans indicated that Spike is technically not a ghost: he lacked ectoplasm, which would make him invisible to human eyes, radiated body heat, whereas ghosts absorb heat and make the area around them a few degrees colder, and had detectable brainwaves, so there seem to be different kinds of disembodied spirits other than ghosts.
Different cultures have adopted different "takes" on ghosts. An example is the Japanese ghosts have no feet and are drawn to water.
Though incorporeal, ghosts and other such non-corporeal beings (with the apparent exception of the First Evil) are capable of limited interaction with the physical world through intense concentration.
- Grace Newman and James Stanley
- Maude Pearson and Dennis Pearson
- Katrina Silber (though it could have been an illusion)
- Willow Rosenberg (temporarily)
- Rupert Giles had mentioned seeing the ghost of a murdered countess in Dartmoor who used to float along the foothills, prior to his Watchers functions.
- Anya Jenkins
- The First Evil is spiritual entity that can take on the form of deceased people.
- The Child of Words demon has an incorporeal form.
- Sineya the First Vampire Slayer after she died, has the power to come to Slayers in their dreams as a spirit guide.