This is a measure of the reflectiveness of an object. An albedo of 1 would indicate a perfect mirror, whilst a perfect black body which absorbs all light falling on it would have an albedo of 0.
The Moon's overall albedo is 0.07. Of its nearside features, Aristarchus is the brightest, with an albedo of 0.18, whilst the floor of Grimaldi is the darkest at only 0.04.