Minimal example of taxonomy terms template?

I have a taxonomy for a term called categories, which I intend to label blog posts with. There are three templates associated with taxonomies:

  • list a content’s taxonomy terms with the single-page template
  • list the content for a taxonomy term with the taxonomy list template
  • order the list of terms for a taxonomy with the taxonomy terms template

The first template seems very clear to me; I’d show all the categories for a post.

The second template also seems very clear to me; I’d list all the posts that belong to a specific category.

The third template, however, is confusing to me. What would that be in this example of categories and posts? And what would a minimal template look like?