IP version 6 (IPv6) is a way of making more room for the vast amount of machines connected to the Internet in some way. Here are resources that can help you learn more about this behind the scenes Web technology:

What is an IP Address?

Learn what an IP address really is in simple terms, as well as the technology behind IP networking and what it looks like from a computer networking perspective.

What does IPv4 and IPv6 mean for Web searchers?

A short and sweet explanation of these two very complicated concepts. Basically, the Internet is running out of room, and IPv6 is going to solve the issue by creating more room for Web addresses. It's something that's been in the hopper for several years and the transition is currently due to happen by the end of 2012. You can read more here: Is The Internet Really Running Out of Room?