A Unique User is a single, unrepeated unit visiting a service in a given period, counted once regardless of the number of visits. In practice it is most often counted per cookie, device and browser, so one person using several devices, or without logged-in accounts, can be counted several times. Actual reach in people is shown only by Real User (RU), which market research firms calculate by statistical methods, extrapolating results to the population. (Compare: Unique Visitors, Visit, Real User)