barn doors

Short definition from Wiktionary

Noun

1. 1
   Four hinged metal slats that come (or are attachable) on the front of cinema lights, used for shaping light and fastening light gels.
2. 2
   Used other than figuratively or idiomatically: see barn, doors.
3. 3
   plural of barn-door

Verb

1. 1
   third-person singular simple present indicative of barn door