United States Magistrate Judge

In the United States federal courts, magistrate judges are judges appointed to assist district court judges in the performance of their duties. Magistrate judges are authorized by 28 U.S.C. § 631 . The position of "magistrate judge" or "magistrate" also exists in some unrelated state courts (see below).

While district judges are nominated by the President and confirmed by the United States Senate for lifetime tenure, magistrate judges are appointed by a majority vote of the federal district judges of a particular district and serve terms of eight years if full-time, or four years if part-time, and may be reappointed. As of March 2009 there are 517 full-time and 42 part-time authorized magistrate judgeships, as well as one position combining magistrate judge and clerk of court.

Magistrate judges generally oversee first appearances of criminal defendants, set bail, and conduct other administrative duties.

Occasionally Presidents nominate magistrate judges for district judge vacancies. The Federal Magistrate Judges Association is the professional association for magistrate judges.

The magistrate judge's seat is not a separate court; the authority that a magistrate judge exercises is the jurisdiction of the district court itself, delegated to the magistrate judge by the district judges of the court under governing statutory authority, local rules of court, or court orders. Rather than fixing the duties of magistrate judges nationwide, the Federal Magistrates Act allows each district court to assign duties to the magistrate judges as fits the needs of that court.

...
Wikipedia