These two numbers get used interchangeably in sales pitches, and the gap between them is exactly where a lot of low-quality link building hides.
The definitions
A backlink is any single hyperlink pointing to your site. A referring domain is a unique website that links to you, regardless of how many individual links it contains. One site linking to you 50 times from different pages still counts as one referring domain.
Why referring domains carry more weight
Search engines treat links from many independent domains as a stronger trust signal than many links concentrated on a few domains. This is precisely why a private blog network, even one spread across dozens of "different" sites, is structurally weak: they're not actually independent, and any tool analyzing common ownership patterns, hosting, or network signals can surface that.
How to evaluate an offer using this distinction
If an agency pitches "50 backlinks," ask how many unique referring domains that represents. A bulk link building campaign spread across 50 genuinely different domains is worth far more than 50 links concentrated on 10 sites.
Common questions on this topic
10 referring domains, almost always. Domain diversity is a stronger trust signal than raw link count.
Ahrefs and Google Search Console both report referring domains separately from total backlinks.
Yes, since it reduces both your total link count and your domain diversity at once.
