Firn is granular snow, especially on the upper part of a glacier, where it has not yet been compressed into ice.
Theoretical firn Edit
Def. "a type of old snow which has gone through multiple thaw and refreeze cycles and thus is made of numerous small icy grains, though it is not nearly as saturated with water as snow-cone slush is; can be hard or somewhat soft depending on recent and current weather conditions" is called firn.
Def. "rounded, well-bonded snow that is older than one year; firn has a density greater than 550 kilograms per cubic-meter (35 pounds per cubic-foot); called névé during the first year" is called firn.