U

UCA
abbreviation for Undercolor Addition, a technique that increases the saturation and vibrancy of an image by adding cyan, magenta, and yellow inks to areas where a lot of black ink is printing. The result is more vibrancy but higher total ink coverage.
UCR
Abbreviation for Undercolor Removal, a technique that replaces equivalent portion of cyan, magenta and yellow ink by black ink, mainly in the neutral parts and the shadows of an image. UCR produces images with a lower total ink coverage than GCR, although the images typically are not as saturated or vibrant. UCR is usually used to produce CMYK images that will be printed on uncoated paper, such as newsprint.
UDP
Abbreviation for User Datagram Protocol
UGR
Abbreviation for Undercolor Gray Removal
UGRA wedge
Special film strip control device that is about 1 inch by 6 inches in size and contains test targets for controlling accurate film exposures on contacts and printing plates. UGRA is a graphic art research association located in Switzerland.
uncalendared
Papers that are not smoothed by going through the calendaring process.
under correction
Insufficient color correction made to compensate for the hue errors of process inks. The result is a reproduction that appears to have one or all hues contaminated with the wrong color. The reproduction will print to dark; the colors will appear to warm or dirty. Under correction is the opposite of over correction.
undercolor addition
A technique that is used to add cyan, magenta and yellow printing dots in dark neutral areas in the reproduction.

under-run –

Term refers to an order produced or delivered that is less than the quantity specified by the customer. Allowances are permitted in trade practices for under-runs.

undertrapping
A color shows through an overprint that was added to hide it.
unicode
Character set that has been created as the universal replacement for ASCII. Unicode can contain either a 16-bit character set (UCS-2, over 32000 characters) or a 32-bit character set (UCS-4, over 4000000000 characters). Unicode can contain all standard Western characters (the alphabet, numbers, all accents,..) as well as the character set of Oriental and Eastern languages (e.g. all Japanese and Chinese characters).
unidirectional
a mode used in printers so they only print when the printhead is moving in a certain direction. If it prints when going both from left to right and from right to left, the system is printing bi-directional.
uniform color space
A 3-dimensional color space in which all pairs of colors that are judged to be equally different are separated by nearly equal distances
uninterruptible power supply
A device that automatically powers a computer without delay when the main power supply fails. The reverse power may be continuous, or it may be only enough protection to allow for an orderly shutdown to avoid data loss.
unit system
A counting method that assigns proportional units or width, based on the EM to each typeface character. Different applications use different unit divisions: 8, 16, 32 and 64 are common. One unit is a thin space or a hair space.
UNIX
Operating system that was developped by AT&T about 25 years ago. Originally it was used for very powerful computers but nowadays it is also fairly popular on personal computers. MacOS X is based on Unix and Linux resembles it a lot.
unsharp masking
A filter in scanner drivers and image manipulation programs like Photoshop that increases the contrast at the edges of density or color changes by exaggerating the differences. Inappropriate use of this filter can lead to images that look artificial.
unwanted colors
Process colors that should not be present in certain areas of a reproduction, such as cyan in yellow or magenta in greens.
up
A general term used to indicate that multiple pages are printed in one impression on a single press sheet. “Two up” or “four up” means printing two or four pages on each sheet. The term is also used when the same image (e.g. a greeting card) is printed multiple times on a sheet.
UPC
Abbreviation for Universal Product Code, a 10-digit code used to label retail products
uplink
An earth station that can transmit a signal to a satellite above the earth.
uploading
The act of copying a file to a network or server from an individual computer
upright
A term given to books bound on the longer dimension.
UPS
Abbreviation for Uninterruptible Power Supply, a battery that keeps a computer system running during a power outage
URL
Abbreviation for Universal Resource Locator, an address that identifies a page on the web (http:/www.prepressure.com/ is the URL of this web site)
USB
abbreviation for Universal Serial Bus, a standard for data transmission between a computer and peripherals like digital cameras, keyboards, scanners or mice.
user-defined keys
Keys that can be programmed to mean any combination or string of characters desired.
user-friendly
A term that is used very loosely to describe computer operating systems and applications that are easy to learn and use.
users group
A club or association whose members share an interest in using a specific computer, application or system.
USM
Abbreviation for UnSharp Masking
utility
A type of software that is used to do a specific small job, such as count the words in a file, or run a small calculator or clock. Good utilities are invaluable to enhance the basic computer system.
UTP
Abbreviation for Unshielded Twisted Pair, a type of cabling used for telephones and computer networks.
UUC
Abbreviation for Universal Copyright Convention – set of rules for the  protection of authors or originators of text, photographs or illustrations etc, to prevent use of their work without permission or acknowledgment. The publication should carry the copyright mark, the name of the originator and the year of publication.
UV coating
A glossy coating that is applied to a printed sheet or part of a page, then bonded and cured with ultraviolet light.
UV ink
Abbreviation for UltraViolet ink, a special ink that dries quickly through the use of ultraviolet light on the press. This allows for more productivity because there is not need to let the ink dry before printing the other side. The inks are aggressive and will shorten the lifespan of the plates used.
UV resistance
The resistance to the fading of colors under direct sunlight