A Unique Visitor count is a metric used in SEO that tells you how many individual users visited a website. While tracking the number of Unique Visitors is an effective way to evaluate your site’s SEO, remember that this is more of a measure of the number of different computer’s accessing a site than of individual people. So the metric can be skewed by individual users who use multiple computers to access the same site (e.g. a person who views a site at home, work, and on their phone) or by individual computers that are used by multiple users (e.g. computers in a library).