card index
countable noun: A card index is a number of cards with information written on them which are arranged in a particular order, usually alphabetical, so that you can find the information you want easily.
card index in American English
card file
noun: a file or catalog consisting of cards on which information has been entered so that desired items or data can be readily found
card index in British English
noun: an index in which each item is separately listed on systematically arranged cards
verb: to make such an index of (a book)
card-index in British English
to make a card index of (a book)