Individual users as represented by a unique user ID. A unique user ID is not associated in any way with personally identifiable information (PII) so it cannot identify a specific unique individual. Also an individual may be associated with multiple user IDs due to clearing browser cookies or using multiple browsers and multiple devices. Additionally for mobile devices a unique user ID may be associated with multiple device IDs (for example Apple IDFA OpenUDID and others). See reach to learn more about individual users/user IDs.