Section vs. sub-page
A section defines a subsite of the main site in which it is housed. For example, cnu.edu/academics is a section of cnu.edu. When a section is created in Cascade, all the necessary assets are created along with it such as the section's index page, navigation block, and _config block.
A sub-page is a page within the section. For example, cnu.edu/academics/departments is a sub-page of cnu.edu/academics. When a sub-page is created, only the index page for the new sub-page is created.