I remember the day when I went shopping in a local mini market with my little daughter, a 5 year kindergarten learner. After filling all we need in a basket, she put them to the cashier. Almost quickly, the cashier counted all the things and said how much we should pay.

From home, my daughter asked me how the cashier can count so quickly without calculator? She knows the thing what we call calculator, because her mom often used it. I couldn't give good answer at that moment.

Another day, when we went to another mini market, I asked her to watch how the cashier count the things that we bought. She noticed everytime the cashier put the things into a scanner.
From home, with her cute little smile, she asked me again (I hoped I could satisfy her with my answer).
"Abbi, (she used to call me this way) What is it?" she pointed the barcode in the back of a chocolate bar.
"That's barcode." I said
"What is barcode?"Uppps!! I couldn't give good explanation for a little kid about barcode.
"Yaaa, it is a barcode. A symbol to differ something." I knew she was not so impressive with my answer.

To make better answer and to avoid more curiousity of my daughter, I searched in the net. I found better information. Honestly, I knew nothing about barcode.
According to Wikipedia, barcodes represents data in the widths (lines) and the spacings of parallel lines, and may be referred to as linear or 1D (1 dimensional) barcodes or symbologies.

Barcode (like in the picture above), applies bars which have black and white colour. Black represents number zero (0) that will absorb the light from barcode reader, and in contrary, white represents one (1) that will reflect the light. So, each bar represents number 1 (one) and empty space represents 0 (zero). American Standard Code for Information Interchange (ASCII) forms 7 digits binary code to open the barcode.
Each barcode has a space for 113 lines (bars). Because it uses 7 digits binary code, One group of 7 bars (including blank spaces) represents 1 (one) number. Besides, it may also symbolize alphabet or special characters, such as; + , $ , etc. Moreover, the thickness of the bar also represent certain value.

The use of Barcode

1. To classify or identify goods, books, cards, or else accurately and quickly
2. In super market, department store, mall, barcode helps much to recognize the price quickly
3. In a library, it helps the librarian to recognize the identity of the books (ISBN - International Standar Book Number).
4. And still so many usage ....
   

Barcode Diagram

• 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.

Types of Barcode

UPC A: Uniform Product Code version A is 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, candies, and so on.
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
PostNet: Barcode used by the United States Postal Service to automatically sort mail. The code is made with evenly spaced bars of two different heights.
Code 39: Code 3 of 9 is a variable length symbol commonly used in military and health applications (like in their ID card).
Code 128: Full alpha-numeric barcode that supports both upper and lower case characters.
Data Matrix: Two-dimensional barcode which can store 2,000 ASCII characters. It can encode a lot of information in a small space.
Maxicode: 2D symbology used by UPS to sort and track packages. This barcode can read at extremely high speeds.




References:
Wikipedia
Barcodeart (dot) com
Kaskus (dot) com