Longman Dictionary of Contemporary English
Wiktionary
n. A piece of heavy paper stock used to record information to be stored in an index.
Wikipedia
An index card (or system card in Australian English) consists of card stock (heavy paper) cut to a standard size, used for recording and storing small amounts of discrete data. It was invented by Carl Linnaeus, around 1760.
The most common size for index cards in North America and UK is , hence the common name 3-by-5 card. Other sizes widely available include , and ISO-size A7 . Cards are available in blank, ruled and grid styles in a variety of colors. Special divider cards with protruding tabs and a variety of cases and trays to hold the cards are also sold by stationers and office product companies. They are part of standard stationery and office supplies all around the globe.
Index cards are used for a wide range of applications and environments: in the home to record and store recipes, shopping lists, contact information and other organizational data; in business to record presentation notes, project research and notes, and contact information; in schools as flash cards or other visual aids; and in academic research to hold data such as bibliographical citations or notes. An often suggested organization method is to use the smaller 3-inch-by-5-inch cards to record the title and citation information of works cited, while using larger cards for recording quotes or other data. Index cards are used for many events and are helpful for planning.
Until the digitization of library catalogs, which began in the 1980s, the primary tool used to locate books was the card catalog, in which every book was described on three cards, filed alphabetically under its title, author, and subject (if non-fiction). Similar catalogs were used by law firms and other entities to organize large quantities of stored documents. However, the adoption of standard cataloging protocols throughout nations with international agreements, along with the rise of the Internet and the conversion of cataloging systems to digital storage and retrieval, has made obsolescent the widespread use of index cards for cataloging.
Usage examples of "index card".
But that's a real busy road and we probably had some people coming home from the mall around ten that night,' Corde jotted a note on an index card.
It was a little loose-leaf notebook with a black leather cover, about the size of an index card, maybe a little bigger, but not much more than that.
She held an index card up, handing it to me with a mixture of triumph and relief.
She scribbled a phone number on an index card and passed it to him.
It contained what looked like a safety-deposit key taped to an index card above the words Illinois State Provident Bank, Grace Street.