A book mark is a small object, often made of paper or cardstock, used to mark a specific page in a book. It serves as a reminder of where the reader left off and helps them easily return to that page when they resume reading. Book marks come in various designs and can be personalized or decorative, often featuring illustrations, quotes, or tassels. They are a practical accessory for avid readers and provide a convenient way to keep track of progress in a book.