“Insert Bookmark”  explains how to use a bookmark, but does not give a clear general definition/explanation of "what is a bookmark" (in LO).
Other pages discuss using bookmarks, such as “Managing Bookmarks”  and “Going to Specific Bookmark” , but they do not explain the meaning of bookmark.
There is also an option to export bookmarks to PDF files .
It would be useful to be able to link the word "bookmark" from these pages to a glossary definition.
Bookmark only appears in Writer, so a applswitch would be appropriate.
Seth Chaiklin committed a patch related to this issue.
It has been pushed to "master":
tdf#153739 add "bookmark" to Glossary; make relevant cross-references