Act of leaving out (8)
I believe the answer is:
omission
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">act of leaving out</span>' is the definition.<br/ ><span class="explanation-format__explanation">(I've seen this before)</span><br/ ><br/ >This is the entire clue.<br/ ></span>
(Other definitions for omission that I've seen before include "Failure to include" , "Leaving-out, oversight" , "Lack" , "Something left out or forgotten" , "It may create space" .)