So the description of /r/Bottomless_Vixens is this: for pictures of clothed female models, nude from the waist down. Now I never knew that there was a fetish for girls that aren't wearing anything on their bottom half, but I guess it kind of makes sense now. Anyway, the subreddit currently has more than 35,000 subscribers and is devoted to both professional and amateur content - some of which is submitted by users of the site.
Note that Bottomless Vixens has quite a few rules to help with content quality including direct image linking, no memes, content only being allowed on Imgur/Minus and a couple of others. While it might be a little bit restrictive, I think they only do it to stop companies and the such like from advertising their material there.
/r/Bottomless_Vixens isn't really a hardcore porn subreddit and features mainly images - a few GIFs and videos appear from time to time, but for the most part, it's all photography of girls that aren't wearing pants or panties.