Open framework (7)
I believe the answer is:
lattice
<span class="explanation-format__ClueExplanation">'<span class="explanation-format__original">open framework</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 lattice that I've seen before include "Open framework in pattern" , "Regular arrangement" , "Framework for window" , "Structure with criss-cross strips" , "Regular open structure" .)