Abbreviation: AS = "Aspherical lens elements" (Nikon)

The abbreviations means "Aspherical lens elements"

Explanation from Nikon

Nikon introduced the first photographic lens with aspherical lens elements in 1968. What sets them apart? Aspherical lenses virtually eliminate the problem of coma and other types of lens aberration even when used at the widest aperture. They are particularly useful in correcting the distortion in wideangle lenses. In addition, use of aspherical lenses contributes to a lighter and smaller lens design. Nikon employs three types of aspherical lens elements. Precision-ground aspherical lens elements are the finest expression of lens-crafting art, demanding extremely rigorous production standards. Hybrid lenses are made of a special plastic molded onto optical glass. Molded glass aspherical lenses are manufactured by molding a unique type of optical glass using a special metal die technique.