Obscene material (4)
I believe the answer is:
smut
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">obscene material</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 smut that I've seen before include "Salacious material" , "Soot flake or sexual innuendo" , "Small flake of dirt" , "Pornographic material" , "Dirt or immoral talk" .)