NSFW and you.

Last updated: March 17, 2014; still accurate as of the Sept. 1, 2014 FAQ update
Just a note that you can link to NSFW fics from blog posts only if they're tagged as related to a Mature fic. None of the other NSFW-related rules have been changed in the latest FAQ update, so everything else still stands.

Feb. 23, 2014: Apparently the FAQ was updated after many of the moderator comments below were made, and those comments are not reflected in the updates. As such, I am assuming that they are not official policy for the time being. Unsupported "rules" have been struck through, but left in for future reference. Supporting comments are now date-stamped and sorted chronologically.

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Not all of the NSFW rules have a nice, neat home in the FAQ. Here are all the ones I've run across, with supporting documentation at the bottom of this post.

Illegal Content Restrictions:
-No human, humanized, or anthro characters in sexual situations unless they are stated to be ADULTS

NSFW Links:
-No links to "illegal" content anywhere on the site
-You may link to NSFW stories in blog posts ONLY if the post is tagged with a Mature story. Group links seem to be OK, but it is best to mark them accordingly.
-You can use group folders or user page favorite modules to link to on-site NSFW stories.
-NO offsite NSFW links of any kind, to text or pictures.
-NO links to sites containing NSFW content are allowed ANYWHERE
-NO links from SFW stories or comments to NSFW stories.
-NO links to NSFW stories in blog posts, user pages, or group posts.

NSFW Text:
-Allowed in groups.
-Allowed in properly tagged stories
-NOT allowed in blog posts.

NSFW Images:
-NOT allowed ANYWHERE.
-If it contains anything questionable, including "Excessive cleavage", it's NSFW. So if it can't be included in an EqD art post, it's NSFW.
-Links to NSFW images or sites containing NSFW images are NOT allowed ANYWHERE
-If you need to share a link to such material, use PMs, or (I guess) link to a 3rd party site that links to but does not contain the NSFW images (so 2 layers of links with no NSFW images shown).

[March 17, 2013] Relevant point from the FAQ:

Linking to on-site Mature stories in blogs is only permitted in blog posts that have a mature story tagged.

[Dec 10, 2013] Relevant points from the FAQ:

What are the rules for content in blog posts?
Do not link to any illegal content. [...] Do not post NSFW content. Linking to on-site Mature stories in blogs is acceptable, but you should ideally mark them as such and avoid mentioning anything particularly explicit.

What are the rules for content/behaviour in groups?
Do not link to any illegal content. Do not post any nsfw images.

NSFW stands for Not Safe For Work. Something is NSFW when you wouldn't want your boss, coworkers, or family members to see it. On Fimfiction, this includes:

* Genitalia, exposed or visible through clothing.
* Excessive gore.
* Heavily implied sexual situations.
* Exclusively fetishistic content.
* Excessive cleavage.

As a general rule, if you have to ask yourself it it’s safe, it’s probably not. Ultimately, it is up to moderator discretion as to what counts as NSFW.

[Dec. 5, 2013] Quotes from Obselescence on underage anthro/human characters from this comment:

Human minors being placed in sexual situations is just generally unallowable. "Foalcon" per se, is roughly allowable, given that it does not involve characters that could be classifiable as human.

Underage anthros in sexual situations is where the line blurs. [...] Given this, allowing anthro sex with characters clearly below the age of majority is a big liability for Fimfiction, and could put the site in a sketchy situation if anyone comes knocking on the door about it.

[...] Regarding underage ponies x adult humans, those aren't currently banned. There was a little ambiguity over that until knighty was able to clarify the matter. Sorry for the confusion.

[Nov. 7, 2013] Quotes from knighty about linking from this post:

[A]s of now linking to nsfw stories from a sfw story (whether in the comments, description or chapter), a blog post, or a group thread is forbidden. Linking to any off site nsfw material is ALSO forbidden in these places [...]

You can't link to NSFW content or stories from your user page either. You are allowed to put Mature stories in your Favorites/Featured Stories module, though, since those won't show up to users with Mature content switched off.

[Oct 29, 2013] Quote from Alexstrazsa in the FAQ update post's comments:

Can you give us an example of something that is just safe enough to post so that we know where the line is?

This is fine: https://derpiboo.ru/454314

[Oct 29, 2013] Quotes from Obselescence in the FAQ update post's comments:

You can make blogs linking to Mature stories on-site, but you should ideally mark them as such and avoid mentioning anything particularly explicit.

Linking to a NSFW image/place where you're going to see a bunch of NSFW images is functionally equivalent to just embedding a NSFW image on the page, so that'd be a no-no too.

Sadly, no. Linking folks to NSFW tumblr blogs isn't a cool thing people can do anymore.

In regards to how bad a tumblr has to be to get blacklisted, it's probably not a big deal if there was like one NSFW post two years ago, but if scrolling through a few pages of the tumblr is in any way likely to show you some naughty content, you should refrain.

Comments

[Cerulean Starlight]

Thank you very much for the information.

[Journeyman]

Now something like this needs to be linked or posted in the NSFW section in the rules. Those rules are updated more than Java asks to install updates on my hard drive.