Daily Unique Visitor

Daily unique visitor is the count of distinct people who viewed the site at least once on a given day; each person counts once no matter how many times they return.

This metric answers the question of how many people, as opposed to pageviews and sessions which answer how many times, so it is the basis for sizing the real audience rather than its intensity. But daily uniqueness rests on an anonymous identifier held in the browser, and that is the source of two errors: one person arriving on a phone and a laptop counts as two visitors, and someone who clears cookies or uses a private window counts fresh each time, so the number usually runs a little high. Another point is that daily uniques cannot be summed across days to get a weekly unique, because a person who came on three days is counted three times in the sum; the weekly unique must be computed independently and is always smaller than the sum of the days.