Barndoors are adjustable metal flaps attached to the front of studio lights, including spotlights and flood lamps. They allow photographers and videographers to control the direction, shape, and width of the light beam, preventing unwanted light from spilling onto areas of the scene. By shaping and restricting light, barndoors are essential for precise lighting setups in portrait, product, and studio photography, helping create mood, depth, and professional-quality images.