NRFW
Stands for "Not Recommended For Work". It's not explicit Porn but it's still titillating and can cause a rise. It's a "Your Mileage May Vary" with your boss if caught looking at such images. It's between NSFW and SFW, the PG-13 of images.
"Well it doesn't have dick or pussy in it so it's not NSFW, but its still turning me on so it's not SFW, what is it?!"
"It's NRFW: Not Recommended For Work"
"It's NRFW: Not Recommended For Work"