A parallax barrier is a technology used to create a 3D effect on displays without the need for special glasses. It consists of a layer with precisely spaced slits that allow each eye to see a different image, simulating depth. This technique is commonly found in some smartphones and tablets. The main advantage of parallax barriers is that they provide a glasses-free 3D experience, making it more accessible for users. However, the viewing angles can be limited, meaning the 3D effect may not be visible from all positions, which can affect the overall experience.