A bar code (often seen as a single word, barcode) is the small image of lines (bars) and spaces that is affixed to retail store items, identification card,and postal mail to identify a particular product number, person, or location. The code uses a sequence of vertical bars and spaces to represent numbers and other symbols. A bar code symbol typically consists of five parts: a quiet zone, a start character, data characters (including an optional check character),a stop character, and another quiet zone.

A barcode reader is used to read the code. The reader uses a laser beam that is sensitive to the reflections from the line and space thickness and variation.The reader translates the reflected light into digital data that is transferred to a computer for immediate action or storage. Bar codes and readers are mostoften seen in supermarkets and retail stores, but a large number of different uses have been found for them. They are also used to take inventory in retail computer for immediate action or storage. Bar codes and readers are most often seen in supermarkets and retail stores, but a large number of different uses have been found for them. They are also used to take inventory in retail stores; to check out books from a library; to track manufacturing and shipping movement;to sign in on a job; to identify hospital patients; and to tabulate the results of direct mail marketing returns.

A Barcode Symbology defines the technical details of a particular type of barcode: the width of the bars, character set, method of encoding,checksum specifications, etc. Most users are more interested in the general capabilities of a particular symbology.

 Numeric-only barcodes                

Codabar:        Older code often used in library systems, sometimes in blood banks
Code 11:         Used primarily for labeling telecommunications equipment
EAN-13:         European Article Numbering international retail product code
EAN-8:           Compressed version of EAN code for use on small products
Industrial 2 of 5:         Older code not in common use
Interleaved 2 of 5:     Compact numeric code, widely used in industry, air cargo
MSI:                Variation of the Plessey code commonly used in USA
Plessey:         Older code commonly used for retail shelf marking
PostNet:        Used by U.S. Postal Service for automated mail sorting
UPC-A:           Universal product code seen on almost all retail products in the USA and Canada
UPC-E:            Compressed version of UPC code for use on small products

Alpha-numeric barcodes                

Code 128:                 Very capable code, excellent density, high reliability; in very wide use world-wide
Code 39:                  General-purpose code in very wide use world-wide
Code 93:                 Compact code similar to Code 39
LOGMARS:                 Same as Code 39, this is the U.S. Government specification

2-Dimensional barcodes                

PDF417:                 Excellent for encoding large amounts of data
DataMatrix:                Can hold large amounts of data, especially suited for making very small codes
Maxicode:                Fixed length, used by United Parcel Service for automated package sorting
QR Code:                Used for material control and order confirmation