Index card
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 3 by 5 inches (76.2 by 127.0 mm), hence the common name 3-by-5 card. Other sizes widely available include 4 by 6 inches (101.6 by 152.4 mm), 5 by 8 inches (127.0 by 203.2 mm) and ISO-size A7 (74 by 105 mm or 2.9 by 4.1 in). 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.