Administration
The back office, at /backoffice/. Where the platform is configured rather
than programmed.
Documentation
The Sourcebook group in the menu holds everything the documentation engine owns: where a source comes from, what an import is waiting for, and the wiki's housekeeping. See Documentation sources for running one, and the Sourcebook dialect for how the content itself is written.
Structure versus configuration
Two menu groups that sound similar and are not:
Structure is what your data is — content types, fields, taxonomy, listings, forms, menus, addresses. Changing it changes what the system can hold.
Configuration is how it behaves — text formats, image styles, PDF and mail templates, maps. Changing it changes how the same data is treated.
When you cannot remember where something lives, ask which of those two sentences it fits.