Perfect score, or half a score (3)
I believe the answer is:
ten
<span class="explanation-format__ClueExplanation">This clue is a double definition.<br/ ><br/ >'<span class="explanation-format__original">perfect score</span>' is the first definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >'<span class="explanation-format__original">half a score</span>' is the second definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ ></span>
(Other definitions for ten that I've seen before include "Half a score" , "Five times two" , "PM's address, Downing St" , "Very young" , "Roman numeral X" .)