Solitary confinement in the United States

In the United States penal system, upwards of 20 percent of state and federal prison inmates and 18 percent of local jail inmates are kept in solitary confinement or another form of restrictive housing at some point during their imprisonment. Solitary confinement (sometimes euphemistically called protective custody, punitive segregation (PSEG) or room restriction) generally comes in one of two forms: "disciplinary segregation," in which inmates are temporarily placed in solitary confinement as punishment for rule-breaking; and "administrative segregation," in which prisoners deemed to be a risk to the safety of other inmates, prison staff, or to themselves are placed in solitary confinement for extended periods of time, often months or years.

Source: Wikipedia — Solitary confinement in the United States (CC BY-SA 4.0)