WordReference Random House Unabridged Dictionary of American English © 2020
snow line′, 
  1. Meteorologythe line, as on mountains, above which there is perpetual snow.
  2. Meteorologythe latitudinal line marking the limit of the fall of snow at sea level.
  • 1825–35

Collins Concise English Dictionary © HarperCollins Publishers::
snow line n
  1. the altitudinal or latitudinal limit of permanent snow
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