Albedo

Part of speech: noun

Pronunciation: /ælˈbi.doʊ/

Definitions

1. The proportion of electromagnetic radiation reflected by a surface rather than absorbed, determining how much light bounces back into space
2. A measure of the reflective quality of any material or celestial object, expressed as the fraction of incident light that is scattered rather than retained
3. The ratio of incoming light or radiation that a surface reflects without absorbing it

Etymology: The Latin root is "albus", meaning white, and it goes back to a Proto-Indo-European root for the same colour, which also gave us words like "alb" and "albumen". English borrowed the noun directly from Latin "albēdō", which means whiteness, so the word began life as a plain description of paleness rather than of light. The modern sense is a scientific one. Albedo measures the fraction of incoming light or radiation that a surface reflects, so fresh snow has a high albedo while dark asphalt has a low one. That shift from a colour to a measured ratio is the main change the word has undergone.