Internet Protocol Address. Every computer connected to the internet has an IP address. Some websites and servers have unique IP addresses, but most web hosts host multiple websites on a single host.

Many SEOs refer to unique C class IP addresses. Every site is hosted on a numerical address like In some cases many sites are hosted on the same IP address. It is believed by many SEOs that if links come from different IP ranges with a different number somewhere in the part then the link may count more than links from the same local range and host.