Length x width (4)
I believe the answer is:
area
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">length x width</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 area that I've seen before include "Speaking formally to (someone)" , "environs" , "Space occupied by something" , "topic" , "land" .)