The Internet Protocol is a communications protocol standard that regulates how data is exchanged between different computers in the public Internet and local area networks (LANs).
An Internet Protocol (IP) address is a numerical identification that is assigned to any device communicating on a computer network or the Internet. An IP-address (IPv4) looks like 22.214.171.124, a combination of 4 numbers from 0-255 seperated by a dot. Because such an IP-address is hard to remember, the DNS service was invented. It maps example.com to the IP-address 126.96.36.199. So if http://www.google.com/ is blocked you can also access the service directly with the IP-address http://188.8.131.52/.
Many lists of Proxies are distributed in the format IP:Port. The IP-address of your local computer is always 127.0.0.1 (sometimes needed for the configuration of some Proxytools). IP-addresses starting with 10.x.x.x, 172.16.x.x-172.31.x.x or 192.168.x.x are private IP-addresses which work only on your local network, not on the Internet.
Because the IPv4 system uses a 32-bit address-system, which theoretically allows only about 4 billion different IP-addresses, the new Internet Protocol version 6 (IPv6) was invented 1998. It works with a 128-bit-system. The number of available IP numbers thereby increases by a multiple. Other advantages of the new Internet Protocol, are the higher security, better support for real-time applications, as well as a higher router performance.
A IPv6 address looks like 2001:0db8:85a3:08d3:1319:8a2e:0370:7334. It is currently not widely used but will chance some important points of both censoring the Internet as well as bypassing Internet censorship in the next years.