In Web marketing, a unique user is, for a specified period of time such as a day or month, an individual that has visited a Web site or received specific content, such as ads, e-mail, or newsletters. For a unique user on a Web site, unique user information consists of, at least, the IP address associated with their computer and a further ID such as a browser ID. Since more than one person may use a computer, other information, such as a user ID and password may be required to ensure that each unique user is being counted. Marketers and Web site owners track unique users to determine how many people see their content within a given period of time. The number of unique users that are served specified content is referred to as that content's reach .
User information can be gathered openly, through registration, or (with or without the user's knowledge) through the use of cookie s. Filtering processes ensure that only humans, rather than bot s, are counted. For further analysis, single unique users, who visit a Web site or see specific content only once, are differentiated from repeat unique users, who visit the site or see the content more than once.