Solitary confinement, colloquially referred to in American English as "the hole" or "the pound" (or in British English "the block"), is a punishment or special form of imprisonment in which a prisoner is denied contact with any other persons, excluding members of prison staff. Punishment is the practice of imposing something unpleasant or aversive on a person or animal usually in response to disobedient or morally wrong behavior A prison, penitentiary, or correctional facility is a place in which individuals are physically confined or interned and usually deprived of a range of Usually cited as an additional measure of protection (of society) from the criminal, it has also been called a form of torture. Torture, according to the United Nations Convention Against Torture, is "any act by which severe pain or suffering, whether physical or mental is intentionally In some cases it is also used to protect the prisoner from others.
Those who accept the practice consider it necessary for prisoners who are considered dangerous to other people ('the most predatory' prisoners), those who might be capable of leading crime groups even from within, or those who are kept 'incommunicado' for purported reasons of national security. Finally, it may be used for prisoners who are at high risk of being attacked by other inmates, such as pedophiles or witnesses who are in prison themselves. The term pedophilia or paedophilia has a range of definitions as found in Psychology, law enforcement and the popular vernacular A witness is someone who has firsthand knowledge about a Crime or dramatic event through their Senses (e This latter form of solitary confinement is sometimes referred to as protective custody. Protective custody is a type of imprisonment (or care to protect a prisoner (or other person from harm either from outside sources or other prisoners
In the US Federal Prison system, solitary confinement is known as the Special Housing Unit (SHU), pronounced "shoe". FBOP redirects here For the bank holding company see FBOP Corporation. California's prison system also uses the abbreviation SHU, but it stands for Security Housing Units.  In other states, it is known as the Special Management Unit (SMU).
Opponents of solitary confinement claim that it is a form of cruel and unusual punishment because the lack of human contact (and the sensory deprivation that often go with solitary confinement) has a severe negative impact on a prisoner's mental state that may lead to certain mental illnesses such as depression or an existential crisis. Sensory deprivation is the deliberate reduction or removal of stimuli from one or more of the senses Mental disorder or mental illness is a psychological or behavioral pattern that occurs in an individual and is thought to cause distress or disability that is not expected as Existential crisis, derived from Existentialism, is the psychologic panic and discomfort experienced when a human confronts questions of existence 
Interestingly, the punishment factor of solitary seems to be lessened or even eliminated in the case of some prisoners with antisocial or sociopathic personalities. Antisocial personality disorder ( APD) is a Mental disorder.It is defined by the American Psychiatric Association 's Diagnostic and Statistical Whether this is due to the flattened emotional responses present in such cases, or the extreme detachment that typify these disorders, is currently unknown.
Solitary confinement features centrally in novels such as Alexandre Dumas' The Count of Monte Cristo and Henri Charrière's Papillon. The Count of Monte Cristo ( Le Comte de Monte-Cristo) is an Adventure novel by Alexandre Dumas père. Henri Charrière ( November 16, 1906 - July 29, 1973) was a convicted felon chiefly known as the author of Papillon Papillon is a Memoir by convicted felon Henri Charrière. It was first published in 1969 and became an instant bestseller at the time It also features in many movies, including such as Murder in the First, The Great Escape, the 1994 movie The Shawshank Redemption, and televisions series' like the HBO's Oz or Fox's Prison Break. Murder in the First is a 1995 film directed by Marc Rocco about a petty criminal named Henri Young (played by Kevin Bacon) who is put on trial for murder The Great Escape is a popular 1963 War film about the 250 Allied prisoners of war escaping from a German POW camp The Shawshank Redemption is a 1994 American Drama film, written and directed by Frank Darabont, based on the Stephen King Oz is an American Television drama series created by Tom Fontana, who also wrote or co-wrote all of the series' 56 episodes A fox is an Animal belonging to any one of about 27 Species (of which only 12 actually belong to the Vulpes genus or 'true foxes' of small Prison Break is an American action / Serial drama television series that premiered on the Fox Broadcasting Company on August 29 2005