Sui iuris is a Latin phrase that is used in law. Sometimes, the phrase is also spelled sui juris. It literally means of its own right. It is used to say that the legal status of an institution or entity is not comparable to anything else, and there are special laws that say how this institution or entity should work. An example use is in Canon law: The Roman Catholic church say that certain churches are sui iuris. That way the Eastern Catholic churches have their own government, and laws. Despite this, these churches still recognize the Pope of Rome as their spiritual leader.
"The Eastern Catholic Churches are not 'experimental' or 'provisional' communities; these are sui iuris Churches; One, Holy, Catholic and Apostolic, with the firm canonical base of the Code of Canons of the Eastern Churches promulgated by Pope John Paul II."