Everything in your mind is private by default.
But sometimes, you'll open mymind in a public space. Or you may want to show something to a coworker or friend, on a screen share or in person. If you don’t want them to see the deepest secrets of your mind, you can hide those cards from your overview and search results.
Just add the tag NSFW to a card and it will no longer show up unless you search that tag.
The tag Hidden and Private do the same. It's perfect for the sensitive bits of info (logins, screenshots, personal manifestos, etc.) you don't want anyone to glimpse over your shoulder.
When you want to find it again, search Private to see all your hidden cards. To un-hide a card, just remove the tag.
Because nobody needs to see that series of nude self portraits you painted entirely with marinara sauce.
At least, until you want them to.