Bar codes, also known as Universal Product Codes (UPCs), are a type of machine-readable code used to identify products. They are made up of a series of black bars and white spaces that represent numbers and letters. The term 'bar codes' is derived from the fact that the code consists of a series of vertical lines, or bars, of varying widths. Bar codes are used in many industries, including retail, manufacturing, and healthcare, to track and identify products. The four letter word for bar codes is LAWS.