Ghost

"A ghost, as I trust that you are all aware by now, is the imprint of a departed soul left upon the earth..."

- Professor Severus Snape

A ghost is the disembodied spirit of a once-living wizard or witch. Only magical beings can become ghosts. Many ghosts take up residence within Hogwarts Castle. These fleshless spirits were either afraid of death or have some extraordinarily strong connection to the locations they haunt.

Physical appearance
In their paranormal state, ghosts are unable to have much physical influence. They are visible, and appear as a greyish-silver apparition of their former (living) selves. They pass through solid objects without damaging themselves or the material, but create disturbances in water, fire and air. The temperature drops in the immediate vicinity of a ghost. Their appearance can also turn flames blue.

Nature
"Wizards can leave an imprint of themselves upon the earth, to walk palely where their living selves once trod... But very few wizards choose that path."

- Sir Nicholas discussing ghosts with Harry Potter

A ghost is the transparent, three-dimensional imprint of a deceased witch or wizard, which continues to exist in the mortal world. Muggles cannot come back as ghosts, and the wisest witches and wizards choose not to. It is those with 'unfinished business', whether in the form of fear, guilt, regrets or overt attachment to the material world who refuse to move on to the next dimension.

Having chosen a feeble simulacrum of mortal life, ghosts are limited in what they can experience. No physical pleasure remains to them, and their knowledge and outlook remains at the level it had attained during life, so that old resentments (for instance, at having an incompletely severed neck) continue to rankle after several centuries. For this reason, ghosts tend to be poor company, on the whole. They are especially disappointing on the one subject that fascinates most people: ghosts cannot return a very sensible answer on what it is like to die, because they have chosen an impoverished version of life instead.

Depending on the conditions of the person's soul, they may not be able to return, as Tom Riddle's self-mutilated soul is trapped in limbo for eternity and cannot become a ghost.

Abilities
In passing through an object, they may impart a sensation of icy coldness. However, they are apparently moved by gusts of wind, as demonstrated when a petrified Nearly Headless Nick was wafted to the Hospital Wing by a large fan, although this may have been possible due to his petrified state. Ghosts are either capable of, or pretend to be capable of, almost being able to taste rotten food.

They are also weightless and may fly in any direction. Ghosts cannot be destroyed, however, they may be petrified with the gaze of a Basilisk. This can be reversed by a Mandrake Restorative Draught, although the method of administration is unclear. Ghosts may also be repelled by magical light, and therefore will retreat from a Wand-Lighting Charm. Ghosts can also be frightened and retreat from a Skurge Charm, which will also clean up any ectoplasm that they have precipitated.

Ghosts in the wizarding world
Witches and wizards are much more susceptible to what Muggles call paranormal activity, and will see (and hear) ghosts plainly where a Muggle might only feel that a haunted place is cold or 'creepy'. Muggles who insist that they see ghosts in perfect focus are either a) lying or b) wizards showing off — and in flagrant breach of the International Statute of Secrecy.

The Ministry of Magic seems to have at least a degree of power and jurisdiction over ghosts, as Moaning Myrtle was forced to return to her place of death, which was Hogwarts School of Witchcraft and Wizardry, when she disrupted the wedding of the brother of Olive Hornby. The Spirit Division is the division of the Department for Regulation and Control of Magical Creatures deals with ghost welfare.

Ghosts also appear to celebrate their deathday, as Nearly Headless Nick did so on October 31st in 1992. They tend to be very sensitive concerning the circumstances of their death, often showing great hesitancy when asked by others how they died.

House ghosts
"About twenty ghosts had just streamed through the back wall. Pearly-white and slightly transparent, they glided across the room talking to one another and hardly glancing at the first years."

- Harry's first experience viewing ghosts at Hogwarts.

Each House at Hogwarts has a patron ghost. Each of these ghosts once belonged to their corresponding House. They apparently serve as a representative to their House, as well as serving the role of messenger or guide to those who are still unfamiliar with the House they were sorted into. It is unknown for how long they may retain this title.

Gryffindor
"I know nothing of the secrets of death, Harry, for I chose my feeble imitation of life instead..."

- Sir Nicholas

The Gryffindor house ghost is Nearly Headless Nick. He is known as a friendly ghost who was nearly beheaded, but the job was poorly executed, which was how he obtained the nickname of "Nearly Headless Nick". He prefers to be addressed as "Sir Nicholas". His real name is Sir Nicholas De Mimsy-Porpington.

Hufflepuff
The Hufflepuff ghost is the Fat Friar. He is known for being friendly and jolly to all. He also frequently suggests that Peeves should have a second chance, whether or not he deserves it.

Ravenclaw
The Ravenclaw house ghost is the Grey Lady, also known as Helena Ravenclaw. She was the daughter of Rowena Ravenclaw, making her the only house ghost to be directly related to one of the four Hogwarts founders. She is renowned for being instrumental in assisting Harry Potter in the search for the Horcruxes.

Slytherin
The Slytherin house ghost is the Bloody Baron. He is well known for being extremely unsocial and many students, including those of his own House, are known to be slightly afraid of him. The Baron is also the only one known to be able to control Peeves. The Bloody Baron is responsible for the death of Helena Ravenclaw as well.

Known ghosts

 * Bloody Baron
 * Professor Cuthbert Binns
 * Fat Friar
 * Helena Ravenclaw (a.k.a. the Grey Lady)
 * Myrtle Warren
 * Lord Draben
 * Sir Nicholas de Mimsy Porpington
 * Sir Patrick Delaney-Podmore
 * Edgar Clogg
 * Wailing Widow
 * Ghost at Gryffindor Tower
 * Knight with an arrow sticking out of his forehead
 * Ragged man wearing chains
 * Portly ghost
 * Ghost of a highwayman
 * Unidentified ghost (VII)
 * Gloomy nuns
 * Unidentified ghost horse (I)
 * Unidentified ghost horse (II)

Behind the scenes

 * In the video game Harry Potter: Quidditch World Cup, a ghost named Edgar Clogg haunts the Quidditch pitch and provides coaching.
 * Professor Amberose Swott may have become a ghost after death as he appears in a portrait at Hogwarts, but also on the Marauder's Map.
 * According to W.O.M.B.A.T., ghosts may have the ability to move liquid or gas.
 * The ghosts Edmund Grubb, the Black Knight and The Toad were cut from final drafts.
 * It is possible that while ghosts might be silver-greyish to the living, it is possible that through their eyes, they see themselves and each other the way they looked alive, as Nearly Headless Nick was able to read a Ghost letter that appeared to be transparent to Harry, meaning that he could not see any written text on it, even if Sir Nicholas could.
 * Although Killing rips the soul, true remorse can heal it again. One example would be the case of The Bloody Baron as he killed Helena Ravenclaw, but felt remorse over her death, thus he was able to come back as a ghost.
 * The house ghosts are known to have died in different time periods. The Grey Lady and the Bloody Baron both died shortly after the founding of Hogwarts. Sir Nicholas died in 1492. It's unknown when the Friar died. Thus, it's not known at which point in Hogwarts history the house ghost position was created or if other ghosts ever held this title.
 * On, there is a feature called "The 6 best-loved ghosts (and one poltergeist) at Hogwarts."
 * According to Rubeus Hagrid, many ghosts like lily flowers.
 * According to, ghosts exist worldwide. Most ghosts reside in Great Britain. And the most haunted place in Great Britain is Hogwarts Castle.
 * The presence of a ghost turns flames blue, according to Pottermore. In the muggle world, a blue flame is very hot, hotter than yellow ones. Ghosts are, however, described as making the environment cold.
 * Unlike other ghosts in the films, the Grey Lady is able to turn into an wispy ball of light.

Appearances

 * Harry Potter and the Philosopher's Stone
 * Harry Potter and the Philosopher's Stone (film)
 * Harry Potter and the Philosopher's Stone (video game)
 * Harry Potter and the Chamber of Secrets
 * Harry Potter and the Chamber of Secrets (film)
 * Harry Potter and the Chamber of Secrets (video game)
 * Harry Potter and the Prisoner of Azkaban
 * Harry Potter and the Prisoner of Azkaban (film)
 * Harry Potter and the Goblet of Fire
 * Harry Potter and the Goblet of Fire (film)
 * Harry Potter and the Order of the Phoenix
 * Harry Potter and the Order of the Phoenix (video game)
 * Harry Potter and the Half-Blood Prince
 * Harry Potter and the Half-Blood Prince (video game)
 * Harry Potter and the Deathly Hallows
 * Harry Potter and the Deathly Hallows: Part 2 
 * LEGO Harry Potter: Years 1-4
 * LEGO Harry Potter: Years 5-7
 * Harry Potter: Quidditch World Cup
 * Pottermore
 * Harry Potter: The Character Vault

Notes and references
Fantasma Fantôme Duch