From Halopedia, the Halo wiki
Templates that are not meant to be used on articles or mainspace pages, and are instead used to extract common functionality to prevent unnecessary code duplication.
Internal templates are usually named with the prefix
Internal/, even when they are part of another set of templates. This is done in the interests of streamlining the editor experience, as it means that search results and LinkSuggest results for a given template won't include irrelevant internal templates that aren't likely to be what the user is looking for. For instance, the template
Template:Internal/Ref/Format won't appear in a link autocomplete when typing
This category has the following 3 subcategories, out of 3 total.