Training unit (3)
I believe the answer is:
rep
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">training unit</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 rep that I've seen before include "Corded cloth for short theatrical group" , "Material for curtains" , "Repertory theatre" , "Stuff" , "Salesperson" .)