A card is a small, flat piece of stiff paper or cardboard with information or images printed on it. Playing cards have numbers, suits, and sometimes pictures of kings and queens. Baseball cards show photos of players with their statistics on the back. Birthday cards carry messages and wishes inside. Business cards display someone's name and contact information so people can get in touch later.

The word appears in many contexts. When you card wool, you comb and straighten the fibers before spinning them into yarn (the tool that does this is also called a card). At certain stores or events, if someone cards you, they're checking your identification to verify your age. People might describe someone funny as a card.

Cards have shaped how we play, communicate, and organize information for centuries. Before computers, libraries used card catalogs, file cabinets filled with thousands of cards listing every book. Today we still carry cards in our wallets: library cards, credit cards, student ID cards. The rectangular shape, perfect for holding in your hand or storing in a pocket, made cards incredibly useful long before anyone invented computers. When magicians shuffle and fan out a deck, or when you sort your trading cards by rarity, you're using an object humans have relied on for hundreds of years.