Longman Dictionary of Contemporary English
cutting room
noun
EXAMPLES FROM CORPUS
▪ Back at the station, the film was rushed into the cutting room and we caught the programme.
▪ Industry shake-ups cursed Earth Girls with a protracted delay between the cutting room and the screen.
▪ It was the latter which still found itself on the drawing board when the rest had hit the cutting room floor.
▪ They are like scraps from a tailor's cutting room which have taken clumsy wing.
▪ Unfortunately, that sentence ended up on the cutting room floor.
Wiktionary
cutting room
n. (context cinema English) A room in which a film is edited to its final form.
WordNet
cutting room
n. a room where films or tapes are edited (by cutting out unwanted parts)