Normal Mapping
Is an alternative to bump-mapping which stores the normals themselves on a texture, rather than altering an existing normal using the texture.
The texture stored is in RGB and encodes both the intensity of the normal and it's orientation. The RGB values equate the XYZ axes and a point in this space determines the direction and length of a normal.
Note: You can quickly [see page 32, calculate] a normal-map from a bump-map.
Note: A normal-map is essentially just a more detailed bump-map. It still suffers from the same disadvantages.
See [see page 29, here], notice that the object appears bumpy even though it's a flat space.
This is [see page 30, often used] to encode differences between a simple mesh and an original mesh. The simple mesh stores considerably less polygons and modifies them using a normal map to get the same visual detail as the original mesh.
Normal maps can exist in both Tangent-space and Object-Space, for more see here.