Slipstream?

[Wulfen]

I've seen this genre listed on some submission guidelines, but I'm not entirely sure what that means (or doesn't mean).

My planned series is set in a wild-west-fantasy-steam-punk world, as you may have noticed by some of my pieces of flash fiction. How do I qualify a setting like that when looking to submit? Fantasy? Steampunk? Other?

Any tips here? It's not your typical steampunk setting, at least I don't think so, so I'm curious to hear how others would try to classify it. The reason I ask is some publishers are only looking for certain genres within fantasy/science fiction.