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(measure of reflectance)

Albedo is a measure of reflectance, i.e., the fraction of incoming light (or any electromagnetic radiation (EMR)) that is reflected. The Earth's albedo varies over the planet and conditions: water versus land, snow cover, cloud cover, city versus country, forest versus desert.

The general albedo of a planet or moon can be inferred from calculated incoming versus observed outgoing EMR, and provides clues regarding its material and atmosphere.

Albedo features are regions on a planet or moon with a noticeably higher or lower albedo than their surroundings. Mars and Mercury show such features.

A body's geometric albedo compares light specifically reflected back toward the source to that which a disk of the same diameter would reflect in that direction if it were a totally diffuse reflector, i.e., if it scattered the reflected light with no preferred direction. Some planet and moon surfaces don't diffuse the light in that manner, reflecting a larger portion straight back at the source (in the manner of a retroreflector such as those used on bicycles and highway signs). There are some such bodies that have a geometric albedo greater than 1.

Further reading:

Referenced by pages:
equilibrium temperature (Teq)
lunar swirl
Mars Science Laboratory (MSL)
phase curve
planet structure
radiative forcing (RF)
transit spectroscopy
water-ice planet