In optics, the Abbe Value is a measure of the degree to which light is dispersed when entering a lens, with high numbers indicating low dispersion or low chromatic aberration. It is named after the German physicist Ernst Abbe who defined it.
Basically, the Abbe Value refers to the clarity of transparent materials. When looking through a lens at a point other than the optical center, the component colors making up white light are displaced laterally by differing amounts resulting in a degraded image, so a challenge in high-index lens design is minimizing effects of chromatic aberration, or color dispersion occasionally noticed by the eyeglass wearer as a halo or color fringes around the edges of an object. A scale used to rate the degree of chromatic aberration of optical materials is the Abbe value. A lower Abbe value indicates more chromatic aberration and a higher Abbe value indicates less.