In English Common Law habeas corpus is the name of several writs which may be issued by a judge ordering a prisoner to be brought before the court. More commonly, the name refers to a specific writ known in full as habeas corpus ad subjiciendum, a prerogative writ ordering that a prisoner be brought to the court so it can be determined whether or not he is being imprisoned lawfully.
The words habeas corpus ad subjiciendum are Latin for "You (shall) have/hold the body to be subjected to (examination)", and are taken from the opening words of the writ in medieval times. Other habeas corpus writs also existed, e.g. habeas corpus ad testificandum ("You (shall) have/hold the body to bear witness", for the production of a prisoner to give evidence in court.
Habeas corpus ad subjiciendum
Known as the "Great Writ", the writ of habeas corpus ad subjiciendum could formerly be used not only in criminal cases, but in cases of imprisonment for private debt. In many jurisdictions today the writ can also be issued against private individuals.
The right of habeas corpus has long been celebrated as the most efficient safeguard of the liberty of the subject. Dicey wrote that the Habeas Corpus Acts "declare no principle and define no rights, but they are for practical purposes worth a hundred constitutional articles guaranteeing individual liberty".
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From Wikipedia
