Which term describes adjustable metal flaps on a lantern?

The term that correctly describes adjustable metal flaps on a lantern is "barndoors." These are specifically designed to control and shape the light emitted from a lantern by allowing the user to open or close the flaps. This adjustability helps in controlling the spread and intensity of the light, creating specific effects or focusing the light on particular areas of the stage.

In contrast, shutters typically refer to a mechanism used to block or cut light in a more static manner, often found in other lighting instruments. Diffusers are materials that soften and scatter the light, providing a more uniform spread, but they do not have adjustable flaps. Reflectors are components used to redirect light, enhancing its output or shaping its path, but they also do not have adjustable features like barndoors.