For example, displaying a list of emergency numbers without any further information about best calling practices or how to report an emergency is a really poor page, more suited to a personal sticky note than a web page.
A simple, uncommented list doesn't provide sufficient content for the user, at least according to chinese overseas british database Google. Neither do copied and duplicated content, auto-generated content, or doorway pages (and rightly so).
Image source: Delante
This manual penalty can lead to partial deindexing of pages that Google considers to be "thin content."