Not legally binding (4)
I believe the answer is:
void
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">not legally binding</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 void that I've seen before include "Null and invalid" , "absence of a suit" , "Null and empty" , "Vacant; not valid" , "Empty space or not legally binding" .)