Texture mapping
Texture mapping is a method of adding realism to a computer generated graphic. Basically, an image (the texture) is added (mapped) to a simpler shape that is generated in the scene, like a decal pasted to a flat surface. This reduces the amount of computing needed to create the shapes and textures in the scene. For instance, a sphere may be generated and a face texture mapped, to remove the need for processing the shape of the nose and eyes.
As graphics cards become more powerful, in theory texture mapping becomes less necessary and 3D rendering becomes more commonplace. Practically, however, the trend has recently been towards larger and more varied texture images. (This is more significant in realtime graphics, where the number of textures that may be displayed simultaneously is a function of the available graphics memory.)