Area of variation (5)
I believe the answer is:
range
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">area of variation</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 range that I've seen before include "Cowboy song 'Home on the . . . . .'" , "Area of variation" , "Cooking stove or location for target practice" , "practise shooting here" , "Chain of mountains" .)