The term for old, compacted snow between fresh snow and glacial ice is firn.
Firn forms when snow survives at least one melt season and is compressed by newer snowfall. Pressure squeezes air from the snowpack, while melting and refreezing can accelerate the transformation. Its crystals become rounded and tightly bonded, giving firn a granular, sugar-like appearance.
Firn is an intermediate stage: fresh snow becomes névé, névé gradually recrystallizes into firn, and continued compression eventually produces dense glacial ice. The boundary or minimum elevation where firn persists is called the firn limit, firn line, or snowline.
Firn is often confused with rime, which is ice deposited directly from fog or supercooled droplets, and with sastrugi, which are wind-carved snow features. Slush is wet, partially melted snow and is not a specific stage in glacier ice formation.