"unf" tag

What exactly is the point of this tag? Seems like it’s just a comment on the image’s content, instead of a descriptor.

I could say that about a lot of tags, like all the dozens of ‘cute’ and ‘sexy’ tags out there.  
I wish they would stop.

Maybe we need a description for it?
 
Something like; “Twilight’s mom”?
 

 
That should do it.
 
Or, perhaps it would be better if Fluttershy explains it.
 

Yeah, there are plenty of images that actually have the word “unf” somewhere in the image
 
but sadly tons of images with the tag that don’t actually contain the word.