A new user discovers a website for the first time by clicking a sponsored link on a search engine results page. One week later, the same user returns to the site by clicking a link from an email campaign. In a report analyzing this second session, what will the dimension First user source display?

First user source reflects the traffic source that first acquired the user. It is user-scoped, so it does not change when the same user returns through a different channel later. The later email visit can appear in session-scoped acquisition dimensions, but it does not overwrite the original first-user value. This distinction helps separate first-time acquisition from later return-session behavior.