What does [UN] or [MUL] mean?

[Deante]

I've seen this tag on thread titles and I'm not sure what it means.

[RampantDesires]

[UN] : If you are undecided or unsure which direction the story will go

I'm not sure what MUL means .. multiple kinks perhaps, though usually the rating goes to the 'hardest' kink. 

[stormwyrm]

Here's a full explanation of all the standard story tags.

[MUL] is not listed though.

[The Dark Raven]

[MUL] usually stands for multiple tags, though I have never seen it (personally) on a single thread before.  Used to see it a lot on request threads that had multiple ideas with different ratings in it.

[Oniya]

It's usually seen on request threads, where the person might have several ideas of varying specific ratings.  For example, they might have one request that's intended to be light, ordinary romance, and another that's a dark non-con.  '[UN]' would be for a plot that could go any direction, depending on what gets hashed out in conversation, but a rating would be decided on prior to making the story thread.