Combining these terms—"index of xxx 3gp"—was a method used by many to find collections of short video clips. In the context of that era, "xxx" was often used as a wildcard search term to find various types of adult content, but it was also used by some as a generic placeholder for specific movie titles or music videos that had been converted for mobile use. Because these directories were often unmoderated, they became hubs for peer-to-peer sharing outside of regulated platforms.
In web terms, an "index of" refers to a directory listing on a web server. Normally, when you visit a website (e.g., www.example.com ), the server delivers a fancy HTML page (like index.html ). However, if a web administrator misconfigures their server and removes the default index file, the server will display a plain, raw list of all files and folders in that directory.
Even if you find a legitimate 3gp file, modern devices struggle with it.