The full form of NSFW is Not Safe/Suitable For Work. It’s used on Miscellaneous ,Chat slang in Worldwide

Not Safe for Work (NSFW) or Not Suitable for Work, is an Internet slang use to mark URLs or hyperlinks which contain material such as nudity, pornography or profanity, which the viewer may not want to be seen accessing in a public or formal setting such as at work.

Content marked NSFW may contain nudity, intense sexuality, political incorrectness, profanity, slurs, violence or other potentially disturbing subject matter. Environments that may be problematic include workplaces, schools, and family settings. NSFW has particular relevance for people trying to make personal use of the Internet at workplaces or schools which have policies prohibiting access to sexual and graphic subject matter. Conversely, safe for work (SFW) is used for links that do not contain such material, but where the title might otherwise lead people to think that content is NSFW.

The similar expression not safe for life (NSFL) is also used, referring to content which is so nauseating or disturbing that it might be emotionally scarring to view. Links marked NSFL may contain fetish pornography, gore or lethal violence