Frozen expanse
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">frozen expanse</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(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" .)