A fragment shader is a type of computer program used in graphics rendering, specifically in the process of creating images on the screen. It operates on individual pixels, or "fragments," generated by the graphics pipeline. The main job of a fragment shader is to determine the color and other attributes of each pixel, allowing for detailed visual effects like lighting, shadows, and textures. In modern graphics applications, fragment shaders are essential for achieving realistic visuals. They work alongside other shaders, such as vertex shaders, to create a complete image. By manipulating data like color and depth, fragment shaders help bring life to 3D models and environments in video games and simulations.