Frozen expanse (6)
I believe the answer is:
tundra
'frozen expanse' is the definition.
(I've seen this in another clue)
This is the entire clue.
(Other definitions for tundra that I've seen before include "Area of permanently frozen subsoil" , "Arctic region of permafrost" , "where you might see caribou" , "Area with frozen subsoi" , "Vast level Arctic region with frozen subsoil" .)