U

UG:

The two-letter designation that precedes the number on connectors for coaxial cable. It is an abbreviation for Universal Government.

UL:

Mark of approval issued by Underwriters Laboratories, Inc.

Ultraviolet (Fiber Optic):

A range of electromagnetic waves in the non-visible spectrum, with wavelengths from 10 to 400 nm (shorter than visible light).

UPC (Fiber Optic):

A term describing a specific fiber optic contact polishing protocol (process), yielding improved return loss.