Place for filming small alien film (3)
I believe the answer is:
set
'place for filming' is the definition.
'small alien film' is the wordplay.
'small' becomes 's' (abbreviation - e.g. clothes size).
'alien film' becomes 'et' (E.T. the Extra-Terrestrial**).
's'+'et'='SET'
(Other definitions for set that I've seen before include "Place - become rigid - adjust - group of tennis games - fixed - clique - fall beneath the horizon" , "Put down tennis games" , "Put, coagulate" , "Class" , "Fix in place; similar group" .)