What are Website Referrers?
When someone creates a backlink to your website this will be indexed by Google or any other search engine, meaning that you'll have an external link to your website.
Referrer URLs are logged by many web analytics programs including Google Analytics. You can monitor these URLs to get insight into where your web traffic is coming from.
This free tool will show you all of the top referrers for your website this is ranked by the amount of backlinks you have on a ceartin website. You can also export all this information to an Excel Spreadsheet.
You can read more about it on this article by Google.