Scrims are metal screen mounted in a metal frame. They are placed in front of a light to reduce light intensity. This is a full double. Arri makes four different types of scrims:
Full single - this scrim covers the entire lightface and reduces the intensity of the entire light beam.
Full double - has two metal screens in it that cover the entire face of the light, reducing intensity by two times the amount of the full single.
Half single - covers only half of the lightface reducing half of the light beams intensity.
Half double - same as the half, single but reduces light intensity twice as much as the half single.