Normal maps are seen as newer versions on bump maps, the similarity being that both create fake detail onto the mesh. A normal map uses RGB information which correlates with the XYZ axis, these tell the program the direction of the surfaces. The most commonly used is called a Tangent Space normal map, this uses a mixture of purples and blues.
Displacement maps are used to detail for low resolution meshes. these maps are created with grey-scale values, you can use 8-bit displacement maps but quality is better when using 16 or 32-bit displacement map. Although these have the best quality displacement maps can be hard on your system, this means that the render time will be longer than using other maps.
Bump maps create detail that is fake, they create an illusion of depth using a simple light trick. Bump maps are grey-scale images that are confined to 8-bits of colour information, that means that there are only 256 different colours of black, white or grey. when grey the maps doesn’t show any detail at all however when pushing up to the white the map starts to show more detail and will pull out from the surface. These maps are better for making small details like wrinkles on skin.