Solitary confinement is a special form of imprisonment in which a prisoner is isolated from any human contact, though often with the exception of members of prison staff. It is sometimes employed as a form of punishment beyond incarceration for a prisoner and has been cited as an additional measure of protection from the inmate or is given for violations of prison regulations. It is also used as a form of protective custody and to implement a suicide watch.

Solitary confinement is colloquially referred to in American English as "the hotbox", "the hole", "lockdown", "SCU" (Solitary Confinement Unit), "AdSeg" (Administrative Segregation), the "SHU" (pronounced 'shoe')—an acronym for security housing unit, or "the pound"; and in British English as "the block" or "the cooler".
In Canada they are known as a Special Handling Unit.