The Collaborative International Dictionary of English v.0.48:

Bookmark \Book"mark`\, n.
   Something placed in a book to guide in finding a particular
   page or passage; also, a label in a book to designate the
   owner; a bookplate.
   [1913 Webster]

WordNet (r) 3.0 (2006):

bookmark
    n 1: a marker (a piece of paper or ribbon) placed between the
         pages of a book to mark the reader's place [syn:
         bookmark, bookmarker]

The Free On-line Dictionary of Computing (30 December 2018):

bookmark

    A user's reference to a document on the
   web or other hypermedia system, usually in the
   form of a URL and a title or comment string.

   Most web and Gopher browsers can save and load
   a file of bookmarks to allow you to quickly locate documents
   to which you want to refer again.

   (1997-06-09)