Not Safe For Work (NSFW) is internet slang or shorthand used to mark links to content, videos, or website pages the viewer may not wish to be seen looking at in a public, formal, or controlled environment.

The marked content may contain;

• Graphic Violence
• Pornography
• Profanity
• Nudity
• Slurs

or other potentially disturbing subject matter. 

Environments that may be problematic include;

• Workplaces
• Schools
• 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 that is so nauseating or disturbing that it might be emotionally scarring to view. 

There are several other terminologies also that are good for us not to know. Having said that there are several websites like Reddit which have a section filled with NSFW content because they ask members to choose while registering if their content is NSFW or not.

There are several other websites on the normal web also that may have discussions with regard to NSFW. For example, black hat world, that has several discussion threads filled with NSFW content. People usually discuss about the ways by which they can make money and they choose the way themselves, and unfortunately several times people choose ways which are not correct.