A barcode is a pattern of parallel black lines and white spaces that computers can read to identify products and track information. You see barcodes on almost everything you buy: cereal boxes, books, toys, clothes. Each pattern is unique, like a fingerprint for that specific item.

When a cashier scans a barcode at checkout, a laser reads the pattern and instantly tells the computer what the product is and how much it costs. Libraries use barcodes to track which books you've borrowed. Hospitals use them to make sure patients get the right medicine. Warehouses use them to know exactly where thousands of items are stored.

Before barcodes were widely used in the 1970s, store clerks often had to type prices in by hand for many items, which was slow and led to mistakes. Now a cashier can scan dozens of items per minute with much better accuracy.

Modern smartphones can scan barcodes too, letting you look up information about products or compare prices instantly.