Referring Domain

A referring domain is the domain name of the site a user clicked through from — example.com, say — extracted from the referrer header.

A referring domain is one level of aggregation over the raw referrer header: instead of the full page URL, it keeps only the domain so all entries from one site fold into a single row. That level makes the domain the right unit for judging partnerships and link-building; you want to know how much that site sends, not how many each of its pages drew. Its key difference from a channel is granularity: dozens of referring domains may all sit in the Referral channel, and to decide on one specific partnership you need the domain level, not just the channel. Its limit is the referrer's limit: if the browser sends no referrer or its policy shortens it, the domain is not recorded at all and that entry goes to Direct.