Albedo is ratio of the light received by a body to the light reflected by that body. Albedo values range from 0 (pitch black) to 1 (perfect reflector).
Geometric albedo is the ratio of a body’s brightness at zero phase angle to the brightness of a perfectly diffusing disk with the same position and apparent size as the body.
Our Moon has a very low albedo (0.07), while Venus has a high albedo (0.60). The albedo combined with the absolute magnitude can help determine the size of an asteroid.