Albedo is a measure of how much energy is absorbed and how much is reflected by a surface. The proportion of incident radiation (e.g. heat from the sun) that is reflected is called "albedo", or "reflection coefficient" and is expressed as a fraction or percentage.

A surface with a high albedo will reflect a lot of the energy that falls on it and so will not warm up quickly.
A surface with a low albedo will absorb lots of the radiation falling on it and so will warm up quickly.

Cloud Albedo
If cloud cover is thick and complete enough, it can form a significant barrier to direct solar radiation.

Ground Albedo
Albedo can also apply to the ground. Snowy ground will have an albedo of approximately 80%, reflecting most solar radiation, whereas trees and ploughed land will reflect less (as little as 20%).
This means that poughed ground will warm up when the sun is shining on it, but snow will stay cold (because it reflects lots of the heat)