Referring Domain

A referring domain is a unique, individual website that contains one or more backlinks pointing to your domain. In off-page SEO, the total number of unique referring domains is a far more critical metric than the total number of backlinks. If a single website links to you 500 times (e.g., a sitewide footer link), Google heavily discounts the value of the subsequent 499 links. Acquiring 500 links from 500 different, highly authoritative referring domains provides exponentially more ranking power and trust signals than acquiring thousands of links from a handful of sites.

Referring Domain Simplified

A referring domain is a single website that links to you. If a popular blog links to you 100 times, that is 100 links, but only one referring domain. Google cares much more about getting links from many different websites than getting hundreds of links from just one.