A password-protected directory is a folder which can't be accessed unless the proper login details are supplied. This may be a whole website or simply a single page that is in a subfolder. If you attempt to open this kind of a directory, you will see a browser pop-up in which you will need to input a username as well as a password. If you enter the correct ones, you can continue browsing the content with no need to do anything else. In case the login details aren't correct, however, you'll see a message that you aren't permitted to view the content. When this option is activated, you won't be able to open a file even if you have a direct link. The option is quite handy if you want to limit the access to some content or if you work on a site and you do not want visitors to be able to access it before it's ready.