Not Safe For Work [NSFW] is a warning next to a link that the content which displays is not safe to display at work: it is a link to strong satirical or sexualized or other manner of politically incorrect content. It may make others uncomfortable or draw undue attention to you when you should be working on your budget spreadsheet. In other words, others may complain about you if you open that link.
Celebrating 25 Years of Creating an Island of Stability In the Sea of Online Confusion