Theater backdrop (7)
'theater backdrop' is the definition.
(I've seen this in another clue)
This is all the clue.
(Other definitions for scrim that I've seen before include "Open-weave muslin fabric" , "material" , "A loosely-woven cotton fabric" .)
(Other definitions for scenery that I've seen before include "Attractive landscape" , "view in the country" , "Theatrical background" , "sight" , "movie sets?" .)