A writ of habeas corpus is a legal order that requires a person who is holding another person in custody to bring the detainee before a court. A writ of habeas corpus refers to (A) a person's right to know the reasons for his or her imprisonment (B) a person's right to not be charged for an action.The writ of habeas corpus primarily acts as a writ of inquiry, issued to test the reasons or grounds for restraint and detention. The "Great Writ" of habeas corpus is a fundamental right in the Constitution that protects against unlawful and indefinite imprisonment. Writ of Habeas Corpus. Know the powers of each specific branch. Habeas corpus is also known as the Great Writ as it preserves the constitutional right to be protected against unlawful imprisonment. Habeas Corpus is when a person under arrest is brought before a judge (chance to show unlawful detention). Writ of Habeas Corpus. Definition. Make "all laws necessary and proper" to carry out the other defined powers of Congress.