What's a pro-zine?
As Dominion's Son said, it's a professional magazine, such as Analog or The Magazine of Fantasy and Science Fiction. In ages past, the major diference between a Pro-zine and a fanzine, aside from Pro-zine being hypenated, was Pro-zines paid ypu money for your story. In general, both had editors who were a little picky about the quality of the story and that it needed to fit into the theme of the zine. In general, Pro-zines tend to continue in publication longer than fanzines do, as fanzine editors gain real lives, while Pro-zine editors, well, it _is_ their life. Right, fanzines. Back in the Olden Days, before the Internet, yea verily in the very dawn of time itself, fanfiction was distributed in fanzines, put together by amateur editors who, in general, raised the funds for the 'zine through advance sale subscriptions; if you wanted to read the next ish [short for issue], you ponied your money up in advance to underwrite the expenses of printing and distribution. Some fanzines were general interest, others were very specific in their focus, such as those devoted to K/S fiction; / fiction, or "slash" fiction, was devoted to non-canon same sex pairings, in this case Kirk & Spock; there was a _lot_ of K/S fic, generally written by women, some of it abysmal, some, so I am told, very well done. Not my scene. Finding out about upcoming fanzines was a bit tricky, but thanks to teh Universal Translator, published by a professor in New York, as I recollect it, there were regular updates on forthcoming 'zines; you had to subscribe to recieve it, and I think you had to pay to be included, but it had a broad distribution and allowed the various SF & F fandoms to keep track of what was coming down the pipe, and who to contact to get your pre-order in. It slowed down just a little when Usenet took off, but not all that many fen had access to Usenet, but Fanzines basically dried up and died once the WWW was developed and became readily accessable; why bother with a fanzine, when you can post your stories online, and read the stories others have posted there? After all, unless the site goes down, they'll be there forever, right? And you don't have to purchase them anymore. *snort* (how naive!) The Fanzine crowd formed the original core of a number of the various fanfiction websites that are still around today, although a number of them were started later by fen unaware of their roots in print society, for whom the words "mimeo" and "corflu" have no meaning; mimeo is short for mimeographic copying machine, an early precursor to modern day xerographic technology, and corflu is short for correction fluid, which was used to cover up mistakes in typewritten originals; "Whiteout" was the most famous brand. yes, this was far in the early dawn of recorded history, for lo! Computers had not yet reached the household, and all of these fanzines were produced on typewriters. "I remember those days fondly," I said, wiping a tear from my face. Not! Well, yes and no. They are long gone, and a part of our past that younger fen don't really comprehend, the world has changed so much. Right, fen, a term used to refer to an active member of SF Fandom. All of these terms, fanzine, Pro-zine, semi-prozine, come out of the SF fan community. A semi-prozine is something like Locus or File 770, kimda sorta maybe? Originally, it was a magazine that published fiction, paying lesss than aprozine, but still more than you'd get by contributing a story to a fanzine; as a result, there were three grades of fiction, fanfic, semipro and pro, with the quality directly bearing on which category they ended up being in, except that fanfiction that was not based upon the authors own creation, but set in another's creation, wasn't going to have a chance in hell of finding its way into a semipro or prozine, due to copyright issues; well, unless they had permission, such as a story published jusr before E.E Smith's death,set in his Lensman universe, it had his approval and was published in Analog. At that time fanfiction hadn't really differentiated between original fiction and derivative fiction to the extent it now has, it used to be a much more unified culture. Even the terminology has morphed, since fanfiction used to just mean fiction by SF fans, and could be original fiction as well as being set in someone else's creation, and now it means fiction by fans of a specific story universe, generally created by someone in the professional media, although stories set in Bill Hart's Spells R Us universe are definitely fanfiction.
Edit: Eep! Good Ghod I'm long winded!