Knald. NormalMap. What is a Normal Map? A Normal Map is usually used to fake high-res geometry detail when it's mapped onto a low-res mesh. The pixels of the normal map each store a normal, a vector that describes the surface slope of the original high-res mesh at that point. The red, green, and blue channels of the normal map are used to control the direction of each pixel's normal. When a normal map is applied to a low-poly mesh, the texture pixels control the direction each of the pixels on the low-poly mesh will be facing in 3D space, creating the illusion of more surface detail or better curvature.
[CG Textures] - Textures for 3D, graphic design and Photoshop! Material Library. GameTextures.com. Blender Cycles - Material Library.