A magistrate has meant many different things in different countries throughout history. The title comes from ancient Rome, where it denoted one of the highest governmental authorities. In some U.S. States, a magistrate is an independent judge. A United States Federal Magistrate Judge is appointed by federal judge and sits in a federal district court. Federal Magistrates serve both civil and criminal cases. In the U.S. there are currently 572 full- and part-time Federal Magistrates. Addressing a magistrate is only slightly different than addressing a judge.
Address the magistrate as "The Honorable," when speaking of the magistrate in the third person, according to the Protocol School of Washington. "Your Honor" or "Judge" would be appropriate when addressing the magistrate directly.
Shorten the title to "Hon." when referring to the judge in writing, as is done by the Federal Magistrate Judges Association.
Address the magistrate directly as "Magistrate Judge" in writing, according to the Indiana University School of Law.