Habeas corpus
Etymology
A Latin phrase meaning "you shall have the body," the opening words of the writ: habeas, the subjunctive of habere, "to have," and corpus, "body." The command directed a jailer to produce the prisoner’s body in court. From those first words the whole protection took its name, becoming a cornerstone of individual liberty in English and American law.
noun phrase · /HAY-bee-us-KOR-pus/
A legal action requiring that a detained person be brought before a court to test whether their imprisonment is lawful.
What it names
The core safeguard against being locked up without justification — the mechanism that forces the state to justify a detention to a judge.
Example
His lawyers filed for habeas corpus, demanding the government show any legal basis for holding him.
Related idea
Habeas corpus tests whether a detention is lawful; a subpoena also compels a person’s appearance, but to give evidence rather than to challenge their own imprisonment.