What is book card?
book card meaning in Information Science terminology / glossary / dictionary is:
A piece of stiff card stock of standard size (three inches wide and five inches high), with space at the top for the call number, name of author, and title of item, and blank lines below for recording the due date and the library card number or name of the borrower, used in manual circulation systems to maintain a card file of items currently checked out. The book card is reinserted in the book pocket inside the item at check-in (see this example). Some libraries use color-coded book cards to indicate type of material or applicable loan rule. See also: date due slip.