A book is a written work typically longer than an article, on the indieweb, there are examples of publishing whole books on indieweb sites, and publishing lists of books.
Jeremy Keith publishes books on his own personal domains in addition to through publishers. E.g.
Erin Jo Richey
Has a page on her site with books she owns: http://erinjorichey.com/library/
Has a page with a few books he knows (either owns/owned or borrowed or read or want to read) on https://seblog.nl/bieb