Important!!!

If you're talking about entering a competition then usually not, some do specify that the stories mustn't have been published anywhere, even posted on a website but usually it should be fine as you retain the copyright on the work. If you have a particular competition in mind then check the rules before posting any stories here. If you're trying to get it published then it should be fine, as you retain the copyright. As Stan the Man says, you'd usually have to delete it from this site once it's accepted for publication elsewhere. If you have a particular publication in mind then check their submission rules before posting any stories here, but as a general rule of thumb you're okay.

Terrence has got it spot on - you retain the copyright to your work and by posting it on here you are, only in one sense, publishing it. It is a very grey area but most people accept that it is not 'previously published'. I hope that helps. Don't freak out - it's Christmas!