Degree of compactness (7)
I believe the answer is:
density
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">degree of compactness</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 density that I've seen before include "Number of items in a given area" , "Compactness - stupidity" , "showing obtuseness" , "Mass/unit vol. (phys.)" , "Closeness" .)