Firn (from Swiss German firn "last year's", cognate with before) is partially compacted névé, a type of snow that has been left over from past seasons and has been recrystallized into a substance denser than névé.- Firn
After deposition, snow progresses on one of two paths that determine its fate, either ablation (mostly by melting) or transitioning from firn (multi-year snow) into glacier ice.- Snow
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Névé is a young, granular type of snow which has been partially melted, refrozen and compacted, yet precedes the form of ice.
Névé that survives a full season of ablation turns into firn, which is both older and slightly denser.