Referring domains is a metric pulled from Ahrefs that lists the total number of unique websites that have one or more backlink pointing toward your website.
According to Ahrefs, there is a direct correlation between organic search traffic and the number of referring domains. This metric gives you the opportunity to determine how many referring domains your website has compared to your competitors.
Not only does it give you an absolute value of your link building, but it also gives you context to the domain rating that you can track over time.
With Pulse, you get access to the information pulled from Ahrefs and allows you to track changes in total referring domains over time.