We call these "links" rather than "referrers" because under this section, we also have outbound links, as well as clicky.me
URL shortener metrics.
"Incoming" links are referrers - when someone clicks a link on another site that leads to your site. Browsers pass this data along and we have access to that data. This is convenient because you know what sites are linking to you and how much traffic those links are generating.
The "Domains" report groups together referrers by domain, so if a site has more than one link to you, you can see the total traffic being generated from that domain in this report.