Albedo is the fraction of solar radiation reflected from the earth and it's atmosphere. The higher the albedo the more reflective an object is. For example, snow has a very high albedo. Albedo is very important for determining positive feedback loops for global warming -- e.g. as the world heats up and snow cover recedes those areas absorb more solar energy and increase the rate of heating. Albedo is also important for the design of solar energy systems.
- Albedo is a unit less number.