underdelivery – Delivery of less impressions, visitors, or conversions than contracted for a specified period of time.
unique visitors – Individuals who have visited a Web site (or network) at least once in a during a fixed time frame.
Universal Analytics – The version of Google Analytics prior to Google Analytics 4 (“GA4”).
URL – Location of a resource on the Internet.
usability – (see Web site usability)
UTM codes – A group of Google Analytics tracking parameters added to the end of URLs to track the effectiveness of marketing campaigns. (UTM = Urchin Tracking Module, from the Urchin analytics software that preceded Google Analytics.)