An iron maiden is a torture

Torture

Torture is the act of inflicting severe pain as a means of punishment, revenge, forcing information or a confession, or simply as an act of cruelty. Throughout history, torture has often been used as a method of political re-education, interrogation, punishment, and coercion...

 device, consisting of an iron cabinet

Cabinet (furniture)

A cabinet is usually a box-shaped piece of furniture with doors or drawers for storing miscellaneous items. Some cabinets stand alone while others are built into a wall or are attached to it like a medicine cabinet. Cabinets are typically made of wood or, now increasingly, of synthetic...

, with a hinged front, sufficiently tall to enclose a human being. It usually has a small closeable opening so that the torturer can interrogate the victim and torture

Torture

Torture is the act of inflicting severe pain as a means of punishment, revenge, forcing information or a confession, or simply as an act of cruelty. Throughout history, torture has often been used as a method of political re-education, interrogation, punishment, and coercion...

 or kill

Capital punishment

Capital punishment, the death penalty, or execution is the sentence of death upon a person by the state as a punishment for an offence. Crimes that can result in a death penalty are known as capital crimes or capital offences. The term capital originates from the Latin capitalis, literally...

 a person by piercing the body with sharp objects (such as knives, spike

Spike

Spike may refer to:-Device to puncture or fasten:* Nail , especially one over ten inches long* Rail spike, or Screw spike used to construct railroad tracks* Tree spiking, making a tree dangerous to cut with a chainsaw...

s or nails), while he or she is forced to remain standing.
The iron maiden is often associated with the Middle Ages

Middle Ages

The Middle Ages is a periodization of European history from the 5th century to the 15th century. The Middle Ages follows the fall of the Western Roman Empire in 476 and precedes the Early Modern Era. It is the middle period of a three-period division of Western history: Classic, Medieval and Modern...

, but in fact was not invented until the 19th century.