For a site...

o whose overall look-and-feel is generated by one php page ("index.php").

o in which "index.php" provides for all pages served the following required components: The DOCTYPE, opening html tag, the head section, the opening body tag, the end-body tag, and end-html tag.

o which uses computed hierarchical navigation menus within "index.php" to offer visitors access to the site content.

o in which all content is stored in individual files that contain "headerless html". (The DOCTYPE, etc. etc. being being provided by "index.php" as described above.)

Q1: what term best describes this architecture?

I'm seeking a concise descriptor that is useful in conversation and definitive as a search term, in whole-web searches, and searching here on Pro Webmasters.

Q2: what term best describes the individual content files?

Same general goals for the descriptor as above. As you see above, I couldn't avoid using the term "headerless html", my best choice. But this term does not seem to be in general use. I've found some people use this term to describe such as my content files, but others use it quite differently.