Referral traffic is the share of visits that came from a link on another site that is not a search engine, social network or tagged campaign. Analytics tools read the HTTP referrer header the browser passes along and attribute the visit to that domain. For SEO, referral traffic shows which backlinks send real visitors, not just link equity.
How referrals are detected
When someone clicks a link, the browser usually sends the address of the page they came from in the Referer header (the header name is spelled that way in the HTTP specification). Most modern browsers default to a referrer policy that sends only the origin, such as https://example.com/, on cross-site requests, so you often see the referring domain but not the exact page.
Unwanted referrals
Some referrals are not real sources. Payment providers, single sign-on pages and your own app domain can appear as referrers when a visitor returns from them, stealing credit from the original source. GA4 lets you list unwanted referrals so those domains are ignored.
- Hosted checkout and payment pages
- Identity providers used for login
- Your own subdomains, if cross-domain measurement is not set up
Referrals that turn into direct
Links from desktop apps, many mobile apps and some email clients do not pass a referrer, so those visits appear as Direct. Links from an HTTPS page to an HTTP page also drop the referrer. This is part of what people call dark traffic.
Example
Valuing a partner listing
Imagine Thornquay, a reporting tool, appears on a partner's integrations marketplace. GA4 shows a steady stream of referral sessions from the marketplace domain with a higher key event rate than organic search. The team prioritizes keeping that listing current and asks the partner to add UTM parameters for cleaner tracking.
Common mistakes
Not excluding payment and login domains
Returning visitors get credited to the payment provider, hiding the real source.
Judging links only by referral sessions
Many valuable backlinks send few visits but still help discovery and authority. Referral traffic is one measure, not the whole picture.
Questions
Referrer spam sends fake hits or visits to get its domain into reports. GA4 filters known bots automatically, but some spam can slip through. Filter it out of your analysis rather than visiting the domain.
