Stereo alternative
I believe the answer is:
quad
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">stereo alternative</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this in another clue)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for quad that I've seen before include "Rectangular area with buildings on all sides" , "One of four children born at one birth" , "Rectangular area surrounded by buildings" , "Sort of bike" , "Square (abbr)" .)