A custodial sentence is a judicial sentence, imposing a punishment (and hence the resulting punishment itself) consisting of mandatory custody of the convict, either in prison

Prison

A prison is a place in which people are physically confined and, usually, deprived of a range of personal freedoms. Imprisonment or incarceration is a legal penalty that may be imposed by the state for the commission of a crime...

 (incarceration

Incarceration

Incarceration is the detention of a person in prison, typically as punishment for a crime .People are most commonly incarcerated upon suspicion or conviction of committing a crime, and different jurisdictions have differing laws governing the function of incarceration within a larger system of...

) or in some other closed therapeutic and/or (re)educational institution, such as a reformatory

Reformatory

Reformatory is a term that has had varied meanings within the penal system, depending on the jurisdiction and the era. It may refer to a youth detention center, or an adult correctional facility. The term is still in popular use for adult facilities throughout the United States, although most...

, (maximum security) psychiatry or drug detoxification

Drug detoxification

Drug detoxification is a collective of interventions directed at controlling acute drug intoxication and drug withdrawal. It refers to a purging from the body of the substances to which a patient is addicted and acutely under the influence...

 (especially cold turkey

Cold turkey

"Cold turkey" describes the actions of a person who abruptly gives up a habit or addiction rather than gradually easing the process through gradual reduction or by using replacement medication....

). For some crimes, such as cases of child sexual abuse

Child sexual abuse

Child sexual abuse is a form of child abuse in which an adult or older adolescent uses a child for sexual stimulation. Forms of child sexual abuse include asking or pressuring a child to engage in sexual activities , indecent exposure with intent to gratify their own sexual desires or to...

, a custodial sentence is almost inevitable.

Although usually not labeled as such (at hence not in the legal sense) it can be considered a type of corporal punishment

Corporal punishment

Corporal punishment is a form of physical punishment that involves the deliberate infliction of pain as retribution for an offence, or for the purpose of disciplining or reforming a wrongdoer, or to deter attitudes or behaviour deemed unacceptable...

, even if no further physical punishments are practiced within the institution (these can also be informal, without any rights of defense), since it constitutes a physical coercion. Indeed the technical term duress is equally used for loss of liberty and for coercion.

The concept of penal harm

Penal harm

Penal harm, an intentionally harsher form of the "deprivation of liberty", is the belief that during custodial sentences , inmates should endure additional pain and suffering, not just having their basic rights taken away, to make the punishment deliberately harder.While this improves the desirable...

 often induces additional elements of physical endurance.

Every other sentence and punishment

Punishment

Punishment is the authoritative imposition of something negative or unpleasant on a person or animal in response to behavior deemed wrong by an individual or group....

is non-custodial, such as fines, judicial beatings, various mandatory but 'open' therapy and courses, restriction orders, loss or suspension of civil rights, or even suspended sentences.