linear barcodes (or 1D), from our supermarket shopping in the 1980's (although the technology was patented in the 1950's). They comprise a series of vertical black lines and white spaces of variable width, representing numbers, which are read (or decoded) by a barcode reader to extract the information they bear.

 

 Most people are familiar with 1D barcodes found on many products at the store or the magnetic stripe on your credit card. These contain a small amount of information which is limited by their length. The 2D barcode stores data along two dimensions so it's capable of containing much more information, easily enough to create a url and a keyword for a query against a database or provide a rich set of parameters to a web service. You may have a 2D barcode on the back of your license if you live in one of the 40 states that have standardized on them. Although it differs by state, it's safe to say that most if not all the information on the front of your license is in the barcode, with room to spare.

There are a host of 2D barcode providers, even one called beetagg that looks like a beehive. Here is a demonstration from shotcode, and yes it looks like a shotgun blast. A company named Augme will even print a 2D barcode on a T-Shirt that will take people to your web site when photographed by a camera phone.