Habeas Corpus, literally means "you have the body," and represents a right granted in the constitution.
Basically, a writ of habeas corpus allows a person to challenge the legality of his detention and requires a prisoner to be brought to court.
The history of Habeas Corpus is ancient and goes back further than the Magna Carta in 1215. The Habeas Corpus Act 1679 is an Act of the Parliament of England passed during the reign of King Charles II.
The name is taken from the opening words of the "Habeas Corpus" writ in medieval times.
Although rarely used nowadays, it can theoretically be demanded by anyone who believes they are unlawfully detained and it is issued by a judge.
It does not determine guilt or innocence, merely whether the person is legally imprisoned. If the charge is considered to be valid, the person must submit to trial but if not, the person goes free.
The Habeas Corpus Act passed by Parliament in 1679 guaranteed this right in law, although its origins go back much further, probably to Anglo-Saxon times.
According to Article One of the Constitution, the right to a writ of habeas corpus can only be suspended in "cases of rebellion or invasion the public safety."
Habeas Corpus was suspended during the Civil War and Reconstruction, in parts of South Carolina during the fight against the Ku Klux Klan and during the War on Terror.
Sources: "Habeas Corpus in America: The Politics of Individual Rights (Constitutional Thinking) by Justin Wert and "Federal Courts: Habeas Corpus, 2d," by Larry Yackle.
Also visit BBC News web site: http://news.bbc.co.uk/2/hi/uk_news/magazine/4329839.stm