Habeas Corpus, in the Federal Court, is a petition that claims that you are being detained against your US constitutional rights. A Writ of Habeas Corpus is a civil proceeding that is available in both State and Federal Court to challenge the legality of imprisonment.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. The writ of habeas corpus primarily acts as a writ of inquiry, issued to test the reasons or grounds for restraint and detention. These are the official forms for use in Family Court proceedings. A Writ of Habeas Corpus. The basis for such an application is DRL §70. The "Great Writ" of habeas corpus is a fundamental right in the Constitution that protects against unlawful and indefinite imprisonment. The "Great Writ" of habeas corpus is a fundamental right in the Constitution that protects against unlawful and indefinite imprisonment. Find definitions for specific words, phrases, and terminology used in the Massachusetts Court System.