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  • Uncertainty Principle
    The fact that conjugate degrees of freedom cannot be simultaneously defined with infinite precision. Rather the product of their uncertainties must satisfy Plank’s constant (h-bar). Examples of conjugate variables include space/momentum, energy/time, and orthogonal orientations of angular momentum.
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  • URL (Uniform Resource Locator)
    A unique address consisting of a string of characters that precisely identifies an Internet resource's type and location. URLs typically have four parts: the first identifies the protocol; the second identifies the domain name; the third identifies the directory path, and the fourth identifies the document file name. Sometimes, the URL includes a fifth part known as the anchor name or bookmark, which points to a specific location within the document file. See also absolute URL and relative URL.
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  • User
    A computer user who is employing a client browser to access Web resources. In the context of ticketing, each user has a user ID encoded in the ticket.
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  • USENET
    A collection of electronic bulletin boards (called newsgroups) set up by subject matter and covering just about every conceivable topic, from molecular biology to nude sunbathing. The newsgroups are organized into hierarchies, such as science (sci), recreation (rec), society (soc), and the miscellaneous category called alternate (alt).
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  • User Credentials
    Information that a user provides to prove his or her identity. In basic authentication, the user credentials are simply a username and password.
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  • User ID
    A number that uniquely identifies a user. Except in the case of anonymous ticketing, user IDs are taken from a registry database accessed by the ticketing agent.
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