CitenzoReferring Domains (RD)
The number of different websites that link to a site. More unique domains usually means more authority.
Referring domains counts how many separate websites link to a page or site — not the total number of links, but the number of distinct sources. Ten links from ten different sites count for far more than ten links from one site, so this is a better trust signal than raw backlink counts.
A high referring-domains number is a sign a site has earned links naturally over time.