If you have ever stumbled upon a plain white webpage listing folder names like Parent Directory, followed by a cascade of file names ending in .pdf, .mp4, or .zip, you’ve encountered an "Index of files."
However, if you want a specific academic paper that defined how modern systems index files efficiently, here is the top recommendation: index of files
Add to .htaccess or virtual host config. Unlocking the Web’s Hidden Blueprint: The Complete Guide
# Enable directory listing
Options +Indexes
These provide better UI, search, and security controls. For text-search indexing: Read Anh & Moffat (2005)
If you are writing a book or long report and need a traditional index of terms: