In the rapidly developing field of photobiology as it relates to solar ultraviolet radiation (UVR), there is a need as never before to ensure that definitions and terminology are current, correct, and standard. This article provides a basic definition of UVR; a review of correct UVR radiometric symbols, units, and nomenclature; defines extraterrestrial and terrestrial solar UVR; and reviews the measurement of biologically effective dose of solar UVR in humans.