A Magistrate was an official who oversaw legal and criminal proceedings.
Magistrates are common under Bajoran law. Deep Space 9 had a magistrate, as did the second Deep Space 9. (DS9 episodes: "Accession", "The Quickening", "Rapture", "Chimera", DS9 novel: The Missing)
In 2323, Syjin was brought before a magistrate in Korto City. (ST - Terok Nor novel: Day of the Vipers)