| UVC | That part of the ultraviolet spectrum nearest to X rays, i.e. short wavelength UV. |
| UVB | Between UVA and UVC. |
| UVA | That part of the ultraviolet spectrum nearest to visible light, i.e. long wavelength UV. |
| UV | Beyond violet. That part of the electromagnetic spectrum which lies beyond the violet end of the visible spectrum, i.e. of shorter wavelength than violet, and invisible to humans. |
| USM | Unsharp Mask. A process used to sharpen images |
| USB | Universal Serial Bus. The most common type of connector to transfer files from digital cameras and scanners. Data transfer speed up to 350 KB/s |
| Unsharp Mask filter | A filter for increasing apparent sharpness of a digital image |
| Unsharp Mask | See USM |
| Underwater Connector | Flash connectors that are specifically for underwater use. |
| under/over | shots that are taken underwater but also have a subject that can be seen through the surface (in Snells' window) |
| Umatic | Sony analog videocassette recording system using helical scanning and 3/4 inch magnetic tape. First appeared mid 1970s. Once favored by industrial training departments, drama schools, etc. but now largely obsolete. |
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