Monochromacy (from Greek mono, meaning "one "and chromo, meaning "color") is the ability of organisms or machines to distinguish only one single frequency of the electromagnetic light spectrum. In the physical sense, no source of electromagnetic radiation is purely monochromatic but can be considered as a gaussian distribution of frequencies shaped around a peak. In the same way, a visual system of an organism or a machine cannot be monochromat but will distinguish a continuous set of frequencies around a peak, depending by the intensity of the light.