The writ of habeas corpus primarily acts as a writ of inquiry, issued to test the reasons or grounds for restraint and detention. The writ of habeas corpus, also known as the Great Writ, is a U.S. legal process that determines whether an offender's imprisonment is valid.Habeas corpus is a Latin phrase meaning "produce the body. This Chapter explains an important right—the writ of habeas corpus. Federal habeas corpus is a procedure under which a federal court may review the legality of an individual's incarceration. Habeas corpus is essentially a safeguard against unjust incarceration. The "Great Writ" of habeas corpus is a fundamental right in the Constitution that protects against unlawful and indefinite imprisonment. What Are the Different Types of Writs?