Sentence:  In the latest issue of Astounding, our old pal and brother-fan, Milt Rothman makes his professional debut under the pen name: Lee Gregor. And Milt is to be congratulated on the story.... it is definitely pro and not <WSD>fan fiction</WSD>. 
Meaning of the word marked with <WSD> tags:  Amateur fiction created by fans, incorporating the characters and concepts of a commercial media property, typically without permission from the author or owner.