What are the "Files" that Metatag module allows adding Metadata to? In Drupal 7, if you go to Configuration &gt; Search and metadata &gt; Metatag &gt; Settings (Tab) the module Metatag allows you to add Metatags to "Files"... What are these files?... As everyone are knows, files are not webpages and I guess there aren't very much good reasons to build themselves as web pages... So why would the module attach them \ associate them with meta tags???
They are all the files managed by Drupal through attachments, images &amp; file fields. In D7, these managed files are entities. As such, the metatag module supports it. 

This isn't useful with the metatag module alone, but if you had a configuration where files had their own display page (e.g. the file entity &amp; media module), it could be utilized.