Attribution
Dark traffic
Also called hidden source.
Dark traffic is visits whose true source the collector cannot see. It is the unknown part of your acquisition numbers.
How it is measured
It shows up as visits with no referrer and no tag, or with a source that does not map to a channel. Causes include privacy settings, app browsers, redirects that drop the header, and untagged links.
Measure its size as a share of sessions. Over time, watch whether the share rises after a redesign, a tag change, or a new app. A steady 25 percent is a different problem from a jump to 45.
Worked example
A garden-tools store sees its unlabeled share rise from 22 to 41 percent of 9,600 sessions after switching its checkout to a new payment page on another domain.
The new page strips the referrer on return and the order confirmation links back as a fresh visit. The shop adds the payment domain to the referral exclusion list, and the unlabeled share falls to 24 percent.
How it differs
Dark traffic is the whole class of unknown sources. Dark social is one cause, private sharing. Traffic can be dark because of a bug and not because of any private share.
Common errors
Treating it as a channel. Ignoring a sudden rise. Not tagging links you control. Letting redirects remove tags. Trying to assign it to a channel by guess.
In practice
Check your unlabeled share this week and set a baseline. Tag every link you send. Investigate any step change after a site change.