The NSFW Section is one of the 5 different ways of uploading content to FunnyJunk. It is not a separate format of content, rather, it is a classification, because NSFW stands for Not Safe For Work, which is a metaphor for anything that wouldn't be allowed at work when someone's on a break. The name is derived form the fact that many workplaces do not allow unsettling images to be viewed at work, thus the NSFW. It does not receive as much views, thumbs, or favorites as other sections, as it is only member-accessible.
While it was originally meant for dirty jokes, now most users only see it as a place for porn.