Binary base (3)
I believe the answer is:
two
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">binary base</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 two that I've seen before include "not very many" , "'It takes ? to tango'" , "Cardinal number" , "Couple, brace" , "Item" .)