Metric area unit (3)
I believe the answer is:
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">metric area unit</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is all the clue.<br/ ></span>
(Other definitions for are that I've seen before include "Unit of land measure equal to 100 square metres" , "Exist; square measure" , "live" , "(We/they/you) exist" , "is for more than one" .)