A strip of material, as of ribbon or leather, or a metal clamp, that is placed between the pages of a book to mark the reader's place. (noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "bookmark" in a sentence
"But my definition of a "bookmark" is very wide - basically anything I can use to stick in the book and mark my place counts."
"To clarify, check the screenshot above to how I set up a keyword bookmark for Lifehacker would look like."
"Slivers of bone in the spine, and the bookmark is made of bleached human hair."