Albedo is an objects reflection coefficient. Albedo is measured as the amount of radiation reflected by an object divided by the amount of radiation originally hitting the object. So the higher the number, the more reflective the object is.
The way in which albedo is measured is on a scale from 0 to 1. 0 means no reflection, so absolutely black, and 1 means perfect reflection, so pure white.
In terms of astronomy, albedo is used to measure the reflectiveness of planets to give us an indication of their surface composition. The albedo of the earth is between 30 and 35%, due largely to cloud cover. In climatology, albedo is used to predict areas of high temperature and areas of low temperature based on cloud cover and the amount of sunlight reflected.
Terrestrial albedo, obviously, is the albedo of the earth. Oceans and forests tend to have low albedos while deserts and cities have fairly high albedos. Over time, humans have come to change the earth’s albedo through clear cutting forests for resources and to make ways for cities. Clearing forests generally increases albedo and would be expected to cause local climate cooling, but other repercussions of clear cutting complicates the matter.