n. 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.
The Century Dictionary and Cyclopedia
n. A name given to snow accumulated in the highest parts of mountain ranges on which glaciers occur, while such snow is in a granular condition, and before, in its downward movement, it has been fully consolidated into ice.
Word Usage
"The line that separates these two areas is called the firn limit or snow line."