I notice a lot of fiction journals consider any online posting of stories a form of publication and disqualify them as a result. But yet I also see that many of us post stories here for feedback (and just to test them on a random audience). If you post a story on a forum, is that considered an exception? With the exceedingly long submission response times of most publications, I can't imagine submitting a story without getting some constructive feedback first. That's too much time to waste on a piece that may not be ready.
It depends. If the story is posted behind a password protected login, many, although not all, publications will not consider that publication, especially if a piece is workshopped. It's always best to check with the venue in question. But if the piece is freely available without a login, then that will usually disqualify it.
in ref of this forum the workshops and competitions are behind a password so probably ( i can't say definitely) aren't considered publication by most journals in the US and UK, other territories may vary the other areas of the forum are publicly viewable and therefore more likely on balance to be considered publication eotd this is an area where individuals have to make their own decisions