In addition to the options in Singular and Archive templates, WordPress and Oxygen provide a few other places which your template can be applied. You can find these options on the Oxygen -> Templates -> Edit screen inside the Other subsection under Where Does This Template Apply?
WordPress has a special page that displays when the root URL is called. This is the Front Page of a website, and WordPress uses its own template for this.
Blog Posts Index
The Blog Posts Index is a Posts archive in WordPress that displays a paginated list of your blog posts.
The Search Results template is used to display the results of a search done with the WordPress search form.
Further reading: https://codex.wordpress.org/Creating_a_Search_Page
When a user tries to access a page that does not exist on your website, a 404 page not found error is returned. Use this template to customize the display of your 404 error pages.
By default, the Inner Content element within any other template uses WordPress content. However, you can create an Oxygen template to be applied to all Inner Content elements across the entire website.
The Catch All template will be applied by default if no other specific template is used. This is useful for template inheritance and to ensure the header and footer are consistent throughout the entire website.