A concept page: one idea, explained on its own, in a few sentences. Chapters
reach these pages through wikilinks such as [[Example concept]], and the
reading site shows them on hover.
The filename is the link target, so it is prose — capitals and spaces are correct here, and a rename breaks every chapter that links to it.
Delete this file once you have concept pages of your own. If you have none,
delete the Definitions folder and the concepts collection in
templates/admin/config.yml with it.