A printed machine-readable code that consists of parallel bars of varied width and spacing. The application most commonly observed is the coding on food and other goods that is read at the checkout and translated into a line of print on the bill showing product and cost. The information is also used to update stock records and provide sales statistics.

In the US the code used for this purpose is the Universal Product Code (UPC) and in Europe it is the European Article Numbering (EAN) code. The UPC decodes initially into two five-digit numbers. The first five identify the supplier and the next five are the item number within that supplier’s range of goods. From this information the checkout terminal can access the details to be printed on the bill. The EAN code has a two-digit number to indicate country of origin, then the two five-digit numbers, followed by a check digit. The EAN arrangement simplifies the allocation of codes to suppliers. Only the two-digit code and the format need to be agreed internationally.

Other codes are used for shop-floor data collection, library systems, and monitoring the circulation of confidential documents. The advantage of bar codes is that they can be produced and read by relatively simple equipment. Codes used for these purposes are Code 39, Codabar, and ‘2 of 5’. See also bar-code scanner.

Two-dimensional (2D) bar codes, e.g. PDF417, are becoming more common but do require a special reader. PDF417 is a two-dimensional bar code that can store up to about 1800 printable ASCII characters or 1100 binary characters per symbol. The symbol is rectangular; the dimensions can be adjusted to grow with the data. There is no theoretical limit on the amount of data that can be stored in a group of PDF–417 symbols.