Left Hand Guard Bars – These bars serve as a starting reference point for the scanning devices.
Number System Character – This digit identifies the type of manufacturer or how the barcode will be used. For example 0, 6, and 7 are generally used in the retail industry, while 3 is assigned to the health and drug manufacturing industries.
Number System Bars – These bars correspond to the Number System Character.
Manufacturer ID Number – Each company must apply for a Universal Product Identification Number with the Uniform Code Council. The UCC assigns each company a unique six digit identification number for use on all of their products. The number is composed of the Number System Character and a five digit manufacturer’s code.
Manufacturer ID Bars – These bars correspond to the Manufacturer’s ID Number.
Tall Center Bar – These bars serve as a middle reference point for the scanning devices.
Item Number – Each company is responsible for assigning a unique five digit number to each of their products.
Item Bars – These bars correspond to the Item Number.
Modulo Check Character – This digit is derived from a mathematical formula based on the unique set of numbers in each barcode that helps ensure the accuracy of the data scan.
Modulo Check Bars – These bars correspond to the Modulo Check Character.
Right Hand Guard Bars – These bars serve as an ending reference point for the scanning devices.

UPC A – Uniform Product Code version A is a widely used style of barcode in retail stores for sales checkout.

UPC E – Version E is a compressed UPC A also called Zero Suppressed. Used on small items like cans of soda, cigarettes, and candy.

EAN 13 – European Article Numbering encodes 13 characters and is used throughout the world (except for USA and Canada) to mark physical goods in retail shops.

ISBN – International Standard Book Number includes the price of the book in the barcode. The last 5 digits in this example translate to $44.95 US dollars.

Data Matrix – Two-dimensional barcode which can store 2,000 ASCII characters. It can encode a lot of information in a small space.

Source (“Barcode Diagram”, Barcode Art)