A bar code is a pattern of parallel black lines and white spaces that contains information a computer can read. You see bar codes on many products in a store: cereal boxes, books, toys, clothes. When a cashier scans a bar code at checkout, the store's computer instantly knows what the item is, how much it costs, and updates the inventory to show one less in stock.

Each bar code is unique to a specific product. The width and spacing of the black bars create a code, similar to how dots and dashes work in Morse code. A special scanner shines a light across the bars and reads the pattern, translating it into numbers and information the computer understands.

Bar codes revolutionized shopping and inventory management when they became common in the 1970s. Before bar codes, cashiers had to type in prices manually for every single item, which was slow and led to frequent mistakes. Now scanning is so fast and accurate that stores can track thousands of products effortlessly.

The term can also be written as one word: barcode. A very common type of bar code on products in the United States and Canada is called the Universal Product Code, or UPC. Libraries use bar codes to track books, hospitals use them to track medications, and shipping companies use them to track packages moving around the world.