Open directories are places on the internet with directories that are unprotected. Normally when you create a new directory on your server you add and index.html or index.htm to it so that a search engine will not simply load the page along with an index of whatever may be in that directory.
https://www.reddit.com/r/opendirectories/
I found that open directories are a hot subject, interesting places where you never know what you will find. At the link above, on Reddit, there is a whole sub-reddit devoted to it. You will find anything from movies, TV series, Software, Music and anything else you might wish to find. You will also run across virus files, hacked files, worms and just about anything else you can imagine; so my advice is run a scan on anything you decide to download and tread carefully. I would post some links here, but they don’t last long. The best thing to do is follow along at the link above…