Here is the list of the Theme files recognized by WordPress. Of course, your Theme can contain any other stylesheets, images, or files. Just keep in mind that the following have special meaning to WordPress — see Template Hierarchy for more information.
The single post template used when a single post from a custom post type is queried. For example, single-books.php would be used for displaying single posts from the custom post type named “books”. index.php is used if the query template for the custom post type is not present.