Ghost
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.
- Compiled partly from Ghost at the Harry Potter Wiki
Description
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.
In passing through an object, they may impart a sensation of icy coldness. Ghosts are either capable of, or pretend to be capable of, almost being able to taste rotten food.
Ghosts also tend to celebrate their deathday. They tend to be very sensitive concerning the circumstances of their death, often showing great hesitancy when asked by others how they died.
They are also weightless and may fly in any direction. Ghosts cannot be destroyed.
As ghosts are imprints of souls of the said deceased wizards and witches, they are unable to move beyond the veil, and are forever trapped in the world of living as intangible beings. Due to this, few would choose this path.
Most things that are very enjoyable to ghosts are ghastly to live witches and wizards. For example, ghosts are said to enjoy the sound of an orchestra of thirty saws.
Only wizards and witches may become ghosts.
Ghosts and the Ministry
Troublesome Ghosts must interact on some level with the Ministry of Magic's Spirit Division. In some cases, Ghosts may be relocated and forced to haunt a particular area, such as befell Moaning Myrtle after disturbing a wedding ceremony.
House ghosts
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.
Gryffindor
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.
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.
