A prisoner is an individual who is held in custody and restricted from leaving a place of detention. In many systems a person suspected of a crime may be taken into custody: for example, someone suspected of murder can be arrested and placed in a prison or jail so they cannot leave before their trial. After a lawful conviction, a court may order imprisonment as a punishment for a specified term, a life sentence, or other measures such as supervised release or community sanctions. Rehabilitation, deterrence and public safety are common stated goals of custody.

The legal classification of someone in custody affects their rights and treatment. Pre-trial detainees are presumed innocent and often have different procedural protections than convicted prisoners. International law provides additional rules for combatants captured during armed conflict: a prisoner of war is a person captured in war and is entitled to protections under treaties such as the Geneva Conventions. Domestic law and human rights norms govern conditions of confinement, access to counsel, medical care and the prohibition of cruel or degrading treatment.

Types and common distinctions

  • Pre-trial detainees: held while charges are pending.
  • Convicted prisoners: serving a court-imposed sentence.
  • Administrative detainees: held for immigration, national security or civil orders rather than criminal sentences.
  • Prisoners of war: captured members of armed forces during conflict.
  • Political prisoners: persons detained for their political beliefs or actions; classification can be contested.

Different jurisdictions use varying terminology—"inmate," "detainee," and "prisoner" are related but carry distinct legal meanings in many contexts. Conditions may range from open facilities to high-security prisons with solitary confinement. The legal regime governing a person in custody shapes what procedures are available, how appeals and parole work, and which oversight bodies may inspect facilities.

Historically, imprisonment as a formal punishment became more common in the modern era as an alternative to corporal or capital punishments. Over time penology—study of punishment—has emphasized rehabilitation, vocational training and reducing recidivism, although practices and priorities vary widely between countries and periods.

Understanding the term "prisoner" therefore requires attention to legal status, the reason for detention, applicable domestic and international law, and the specific conditions of confinement. Debates about prison reform, sentence length, humane treatment and alternatives to incarceration remain central to public policy and human rights discussions.