Prairies (6)
I believe the answer is:
plains
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">prairies</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for plains that I've seen before include "Flat tracts of land" , "Extensive tracts of level open land" , "Large areas of level country" , "Grasslands" , "Prairies" .)