Magistrate judge vs. district judge
Both serve on the U.S. District Courts, but they hold different offices. District judges are Article III judges: nominated by the president, confirmed by the Senate, and appointed for life. Magistrate judges are judicial officers of the district court itself, appointed by the district’s judges under 28 U.S.C. § 631 to renewable eight-year terms: no presidential nomination, no Senate vote.
What each decides
District judges preside over the full range of federal cases, civil and criminal, and enter final judgments. Magistrate judges handle much of the bench’s day-to-day: pretrial motions and scheduling, discovery disputes, settlement conferences, search and arrest warrants, and misdemeanor trials. With the parties’ consent a magistrate judge can preside over an entire civil case, including trial and judgment.
A similar pattern holds for bankruptcy judges: officers of the district’s bankruptcy court, appointed by the circuit’s court of appeals to fourteen-year terms. Browse the district courts and bankruptcy courts. Each court page lists its judges, and each district page lists its magistrate judges in their own section.