A magistrate is a person who lays down the law — a judge or other civil authority who conducts a court. Minor offenses are often brought before a magistrate.
Magistrate goes back to the Latin magistratus, meaning "administrator." Lawmakers and judges might have a role in making and changing laws; magistrates focus on carrying out the laws on a case-by-case basis. A magistrate doesn't usually make final rulings on murders or high-level cases. He or she might hear cases about things like property damage or traffic violations.