A passive shutter is a technology used in 3D displays to create the illusion of depth. It works by alternating the visibility of images for each eye, allowing viewers to perceive three-dimensional visuals. This is typically achieved using special glasses that have liquid crystal lenses, which open and close in sync with the display. In passive shutter systems, the display shows two slightly different images, one for the left eye and one for the right eye. This method is commonly used in conjunction with LCD or LED screens and is popular in cinemas and home theaters for enhancing the viewing experience.