Ultraviolet index. The ultraviolet index or UV Index is an international standard measurement of the strength of sunburn-producing ultraviolet (UV) radiation at a particular place and time. The scale was developed by Canadian scientists in 1992, then adopted and standardized by the UN's World Health Organization and World Meteorological Organization in 1994.
one-quarter-one of four equal parts; a quarter of a pound. fourth part, one-fourth, quarter, quartern, twenty-five percent, fourth. common fraction, simple fraction-the quotient of two integers.
1 A percent is the number of parts out of 100 of something. For example, a quarter (25 cents) is 25 percent of a dollar (100 cents). It is the numerator of a fraction whose denominator is 100.  percent, sometimes written as 25%.