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http://en.wikipedia.org/wiki/Master_(judiciary)

A Master is judicial officer found in the courts of England and in numerous other jurisdictions based on the common law tradition. A master's jurisdiction is generally confined to civil proceedings and is a subset of that of a judge. Masters are typically involved in hearing motions, case management, dispute resolution or adjudication of specific issues referred by judges. Their functions would otherwise fall to the judges of the court.

Besides the courts of England & Wales, masters may be found in the Republic of Ireland, Australia, New Zealand, several Caribbean countries and a number of Canadian provinces. Several state courts in the United States utilize masters or similar officers and also make extensive use of special masters.

http://en.wikipedia.org/wiki/Special_master
In the United States of America a special master is an "adjunct to a federal court, and Rule 53 of the Federal Rules of Civil Procedure allows a federal court to appoint a master, with the consent of the parties, to conduct proceedings and report to the Court.[2]