A referring domain is a unique website that links to your site at least once, regardless of how many individual backlinks come from that same domain. A site could have thousands of backlinks but only a few dozen unique referring domains if many links come from the same sources.
Referring domain count is generally considered a more meaningful authority metric than raw backlink count, since search engines tend to place more weight on the diversity of sites vouching for a page than the sheer volume of links, which can be easily manipulated.
Growing the number of high-quality, relevant referring domains — rather than accumulating many links from the same few sources — is a core focus of sustainable link building strategy.
Referring domain growth is a key metric we track in our Link Building service.