A bump map is a texture used in 3D graphics to create the illusion of depth and detail on a surface without adding extra geometry. It works by altering the surface normals of a 3D model, which affects how light interacts with it. This technique allows for more realistic appearances, such as wrinkles on fabric or roughness on stone, while keeping the model's polygon count low. Bump maps are typically grayscale images, where lighter areas represent raised surfaces and darker areas indicate depressions. They are commonly used in video games and animations to enhance visual quality without significantly increasing rendering time or computational load.