A bar code is a machine-readable representation of data in a visual format on a printed surface. Originally, bar codes were simply identifiers, an alignment of parallel, rectangular bars and spaces which represented a set of characters or numbers. Today, bar codes come in many types some in dot patterns, circles, or even some bar codes that are almost hidden in printed images. Symbology is the mapping that occurs between the messages and barcodes. There are many types of bar code symbologies; but they all encode a string of characters to be optically read by scanners (also called bar code readers) that capture the images and convert them to digital data. Bar codes can be applied to almost any surface of almost any material.
Today, bar codes are practically ubiquitous and are easily the most commonly used AIT method because they are inexpensive. A bar code reader simply scans the bar code, decodes the data by translating optical representations into electrical ones, and transfers that data to a data processor, such as an electronic cash register or a personal computer. While there are dozens of bar code symbologies, only a small subset of these is widely used. For convenience, we can categorize bar codes into three types: