Ultraviolet is the part of the electromagnetic spectrum shown on the left side of the picture below as black—because humans cannot see light of such short wavelength (or high frequency). Many animals such as some insects, some reptiles, crocodiles, salamanders, and small birds can see things that reflect this light. UV is a common abbreviation of ultraviolet, mainly used in technical contexts.
Ultraviolet is beyond the visible violet light in terms of frequency, wavelength, and energy. Its wavelengths are between about 10 nanometers (nm) to about 400 nanometers. Frequency and wavelength are closely related. The equation that shows this relationship is: ν = c/λ . Saying that something has a short wavelength is the same as saying that it has a high frequency.