UDP : (User Datagram Protocol): Transfers information between two applications. Usually used for messages or commands between applications. The data is not guaranteed accurate as with TCP.
Underscanning (Under Scan) : A technique generally used by some TV and video systems as a way of ensuring that the complete image is always visible within a display area; the opposite of over scanning.
URL : Acronym for Universal Resource Locater.
USB : Acronym for Universal Serial Bus. This is standard PC hardware. It allows external devices to be easily connected to a PC, DVR, etc. Connected devices are typically hard drives, CD/DVDs and flash drives.
UTC : This is an acronym for Up-The-Coax. This refers to sending telemetry information (PTZ control data) to a PTZ device on the same coax cable that provides the video. The data is transferred during the Vertical Blanking Interval (that wide black line you might see on a rolling image) and does not interfere with the video display.
UTP : An acronym for Universal Twisted Pair. This refers to any twisted pair wire whether a single pair or four pair as in CAT-5 cable