What makes a Superman comic book a '1st edition'?

A '1st edition' Superman comic book refers to the very first printing of a particular issue. This is typically determined by looking at the publication date, the printing history indicated on the comics themselves (often on the copyright page), and the presence of specific identifying marks like a '1st Printing' or 'First' on the cover or inside. Key factors also include the initial distribution and cataloging information from sources like Overstreet Comic Book Price Guide.