What is the Referrer in the list of Commissions?

As you may have noticed, there is a possibility to show additional columns at Transactions > Commissions via the "Edit view" option.
There are many columns and among them, there is also the "Referrer" column.
The Referrer column contains the HTTP_REFERRER that identifies the page from which the customer proceeded to the thank you (order confirmation) page in which the sale tracking code was triggered. 
In case you wanted to see the page in which the referring affiliate's link/banner was clicked, then you shall enable the First Click Referrer and/or Last Click Referrer columns.
There can be also special cases when the referrer URL is empty.