Definition - What does Unique Visitor mean?
Unique visitor is a term used in Web analytics to refer to a person who visits a site at least once within the reporting period. Each visitor to the site is only counted once during the reporting period, so if the same IP address accesses the site the site many times, it still only counts as one visitor. Special measures are taken by analytical programs to filter out visits that are not human, such as visits from spiders, crawlers and other bots.
A unique visitor is also known as a unique user.
Techopedia explains Unique Visitor
A reporting period may be a few days or several months, so the number of unique visitors will vary depending on the period used. A common period is a month, with unique visitors (or unique visits) per month being a popular metric for setting goals, pricing ads and other important activities. The measurement of unique visits is not perfect, as a single user could visit a site from three different IP addresses and count as three visitors. Also, many different users accessing the same machine would be counted as one (as happens with computers in public libraries).