|Someone is wrong on|
NSFW is an internet warning to people, typically given after an awesome link that will reduce your boredom and make the day worthwhile. It means "Not Safe For Work": i.e., the content may be entertaining in one way or another, but if you go there on your company computer, it will be on your permanent record. And if anyone glances into your cubicle when you're there? Odds are the harassment suit has already been filed.
The term has been popularized through the drunken antics of Drew Curtis.
- Maybe you can get away with boobies on your work computer screen (and permanently in your archived history).
- Maybe you can get away with Nazi imagery on your work computer screen (and permanently in your archived history).
- Maybe you can get away with some crap at RationalWiki (oops, too late!) on your work computer screen (and permanently in your archived history).
Most people can't.
IF IT SAYS NSFW, DON'T GO THERE AT WORK! (Or school, for that matter, although chances are it has already been blocked anyways.)
 For even worse situations
Not Safe For Life (NSFL) is, as Urban Dictionary puts it, "doesn't matter where you view the material; you will be scarred." Common on Reddit for stuff that isn't technically NSFW but is still horrible.