The Universal Product Code (UPC or UPC code) is a barcode symbology widely used worldwide to track trade items in stores. The chosen symbology has bars (or spaces) of exactly 1, 2, 3, or 4 units wide each; each decimal digit to be encoded consists of two bars and two spaces chosen to have a total width of 7 units in both an "even" and an "odd" parity form, which enables being scanned in either direction. Unique "guard patterns" (3 or 5 units wide, not encoding a digit) are intermixed to help to decode. A UPC (technically, a UPC-A) consists of 12 digits uniquely assigned to each trade item.
The international GS1 organization assigns the digits for the UPC and the related International Article Number (EAN) barcode.[1] UPC data structures are a component of Global Trade Item Numbers (GTINs) and follow the global GS1 specification based on international standards. However, some retailers, such as clothing and furniture, do not use the GS1 system, instead using other barcode symbologies or article number systems. Some retailers use the EAN/UPC barcode symbology but do not use a GTIN for products sold only in their stores.