albedo

from WordNet (r) 3.0 (2006)

albedo
    n 1: the ratio of reflected to incident light [syn: {albedo},
         {reflective power}]

from The Collaborative International Dictionary of English v.0.48

Albedo \Al*be"do\, n. [L., fr. albus white.]
   Whiteness. Specifically: (Astron.) The ratio which the light
   reflected from an unpolished surface bears to the total light
   falling upon that surface.
   [1913 Webster]