Definition: Saint is slang for "Saint-Gaudens gold coins." The term Saints almost always refers to the famous U.S. Saint-Gaudens Double Eagle $20 gold pieces, but it can sometimes mean any of the classic gold coins designed by Saint-Gaudens. It does not refer to the modern redesigns, though. Those are called "Gold Eagles" or "American Eagles." Augustus Saint-Gaudens was a world renowned sculptor and important coin designer in the early 20th century.
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In my opinion, buying Saints is a much smarter investment than buying Gold Eagles.