The literal meaning of habeas corpus is "you should have the body"—that is, the judge or court should (and must) have any person who is being detained brought forward so that the legality of that person's detention can be assessed. In United States law, habeas corpus ad subjiciendum (the full name of what habeas corpus typically refers to) is also called "the Great Writ," and it is not about a person's guilt or innocence, but about whether custody of that person is lawful under the U.S. Constitution. Common grounds for relief under habeas corpus—"relief" in this case being a release from custody—include a conviction based on illegally obtained evidence; a denial of effective assistance of counsel; or a conviction by a jury that was improperly selected and impaneled.

The literal meaning of habeas corpus is "You shall have the body"—that is, the judge must have the person charged with a crime brought into the courtroom to hear what he's been charged with. Through much of human history, and in many countries still today, a person may be imprisoned on the orders of someone in the government and kept behind bars for years without ever getting a chance to defend himself, or even knowing what he's done wrong. In England, the right to be brought before a judge to hear the charges and answer them was written into law over 300 years ago, and the U.S. adopted the British practice in its Constitution.