Shader languages are specialized programming languages used to write shaders, which are small programs that dictate how graphics are rendered on the screen. They allow developers to control the appearance of surfaces, lighting, and effects in 3D graphics. Common shader languages include GLSL (OpenGL Shading Language) and HLSL (High-Level Shading Language), each tailored for different graphics APIs. These languages enable the creation of visual effects like shadows, reflections, and textures by manipulating pixels and vertices. Shaders run on the GPU (Graphics Processing Unit), allowing for efficient processing of complex visual tasks, enhancing the overall performance and quality of graphics in video games and simulations.