Territory over which control is exercised (6)
I believe the answer is:
domain
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">territory over which control is exercised</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for domain that I've seen before include "estate" , "Area under someone's control, field of activity" , "Territory over which rule or control is exercised" , "Kingdom or realm" , "Field of thought or activity" .)