The exact meaning of magistrate varies widely depending upon the context. For example:
in the U.S. federal court: assists district court judges by handling minor offenses or administrative tasks such as preliminary hearings (often referred to as a magistrate judge rather than just a magistrate)
in some U.S. states: a judge in the state court
in France, Belgium, Italy, the Netherlands, and other civil law countries: a sitting magistrate is a judge and a standing magistrate is a prosecutor
in England: may be a volunteer without formal legal training who performs a judicial role with regard to minor matters
in ancient Rome: a powerful officer with both judicial and executive power
Elizabeth soon perceived, that though this great lady was not in commission of the peace of the county, she was a most active magistrate in her own parish, the minutest concerns of which were carried to her by Mr. Collins; and whenever any of the cottagers were disposed to be quarrelsome, discontented, or too poor, she sallied forth into the village to settle their differences, silence their complaints, and scold them into harmony and plenty.
Chapter 30 (36% in)
There are no more uses of "magistrate" in Pride and Prejudice.