Referring domain
A referring domain is a single unique website that links to your site, regardless of how many individual backlinks it sends.
If one blog links to your homepage three times and your pricing page twice, that counts as five backlinks but only one referring domain. SEO tools track both numbers separately because they answer different questions: total backlinks measure raw link volume, while referring domains measure how many distinct voices are vouching for you.
Referring domains are usually the more meaningful metric. A profile with 500 backlinks from 10 domains is far weaker than one with 500 backlinks from 300 domains, because search engines apply diminishing returns to repeated links from the same source. Broad, diverse domain coverage signals genuine popularity rather than a handful of friendly or paid placements.
When auditing a link profile, look at the ratio of referring domains to total backlinks and at the quality of those domains (relevance, domain rating, and spam score). A sudden spike in backlinks with almost no new referring domains often points to sitewide link placements or low-value directory spam rather than real editorial coverage.