Referring Domains report shows all domains that link to the researched domain/URL, the number of backlinks earned from individual referring domains, their Page Rank and Trust Rank, and Alexa Rank. The referring domains are sorted in a descending order based on the number of backlinks received from them. You can view all backlinks of a particular domain by clicking on the corresponding figure.

Referring Pages (1) — the number of backlinks earned from a particular domain.  

Alexa Rank (2) — a traffic metric which estimates the domain’s traffic rank based on 3 months of historical traffic data collected from the users of Alexa Toolbar. The algorithm takes into account the domain’s traffic sources, unique visitors, and page views, as well as the number of  visitors and number of page views of all the sites with Alexa Toolbar installed. The lower the score, the more traffic-driving the domain is. NA would indicate that there’s not enough data to calculate the traffic rank for the domain, or the domain doesn’t have the Alexa toolbar installed.

Serpstat Page Rank (SPR) (3) — a score on a scale from 0 to 100 which measures the domain/URL authority. Serpstat Page Rank predicts how influential a domain/URL might be based on the number of pages  linking to it. Links are not measured with equal weight, so a strong link will have a relatively stronger influence on domain/URL.

Serpstat Trust Rank (STR) (4) — a score on a scale from 0 to 100 which measures the domain/URL trust based on how trustworthy domains/URLs are linking to the domain/URL in question. A link coming directly from a trustworthy domain boosts the domain / URL trust score and consequently rankings, while toxic links damage rankings and the trust level.