Unduplicated audience -
The number of unique individuals exposed to a specified domain, page or ad in a specified time period. (See Unique User, Unique Visitor).

Unique browser  -
An identified and unduplicated Cookied Browser that accesses Internet content or advertising during a measurement period. This identification procedure should use an attribution method, generally a cookie identifier, to identify the browser and establish the unduplicated nature of the audience activity during the reporting period. Included here should be an appropriate method, fully disclosed, to account for the potentially inflationary impact of cookie deletion among certain of the cookied browsers that access Internet content.

Unique cookie -
A count of unique identifiers that represents unduplicated instances of Internet activity (generally visits) to Internet content or advertising during a measurement period. Unique cookies do not generally represent unduplicated browsers, users or people accessing Internet content or advertising, due to several complexities surrounding the use of cookies and the accurate linkage of this identifier information to the browsers or users involved. Measurement of unique cookies for primary audience reach metrics by Publishers, ad servers, and those who rely on the identification of cookied browsers to measure audiences is subject to numerous challenges, notably cookie deletion. (See Cookie deletion).

Unique device -
An unduplicated computing device that is used to access Internet content or advertising during a measurement period. A count of unduplicated devices necessarily accounts for multiple browser usage on an individual computer or other computing device. It may also contribute to an understanding of the number of Unique Users, if it informs the number of multiple users who access Internet content that are attributable to a single computer or computing device.

Unique reference number -
A unique number assigned to a list member, usually by the Email-broadcast software, and used to track member behavior (clicks, subscribes, unsubscribe) or to identify the member to track Email delivery.

Unique user/visitor -
An identified and unduplicated individual Internet user who accesses Internet content or advertising during a measurement period. Census-based Publishers and Ad-servers will generally need to rely on algorithms (data models) to estimate the number of users attributable to the counts of Unique Cookies they develop. This is distinct from Syndicated Measurement Organizations that rely solely on panel tracking to derive counts of Audience Reach without the use of cookies. If the measurements include both pulled content and accessed pushed content, they should be referred to as Unique Users. If no pushed content is included, the measurement can be referred to as Unique Visitors. (For additional details, see ‘Audience Reach Measurement Guidelines’ at www.iab.net).

Universal Search -
Also known as blended, or federated search results, universal search pulls data from multiple databases to display on the same page. Results can include images, Videos, and results from specialty databases like maps and local information, product information, or news stories.

Upload -
To send data from a computer to a network. An example of uploading data is sending e-mail.

URL (Uniform Resource Locator) -
The unique identifying address of any particular page on the Web. It contains all the information required to locate a resource, including its protocol (usually HTTP), server domain name (or IP address), file path (directory and name) and format (usually HTML or CGI).

User -
An anonymous person who uses a Web browser to access Internet Web content.

User centric measurement -
Web audience measurement based on the behavior of a sample (panel) of Web users.

User Generated Content (UGC) -
Media that is generated by users of a site, rather than producers of a site.

User-Initiation -
The willful act of a user to engage with an ad. Users may interact by clicking on the ad, and/or rolling over an ad (or a portion of an ad). When a user engages the ad using a rollover action, the user’s cursor must rest on the hotspot for at least one second before any action may be initiated in the ad. See the definition for rollover for more information.

User registration -
Information contributed by an individual which usually includes characteristics such as the person’s age, gender, postal code and often much more. A site’s registration system is usually based on an ID code or password to allow the site to determine the number of unique visitors and to track a visitor’s behavior within that site.