Individuals who have visited a Web site (or network) at least once in a fixed time frame, typically a 30 day period.
Information
Most measurements of unique visitors are estimates.
Sites often calculate unique visitors based on the IP address information
found in the log files, and sometimes through cookies. However, many factors may
skew the results.
Traffic rating companies typically calculate unique visitors by monitoring
actual usage of a group of volunteers, then applying the results to
to the Internet population. Results fluctuate considerably for small
sites due to their small sample sizes.
