Bergerud, here is a section describing the maps.
A displacement map is real geometry (polygons), while a bump map is tricks of light to make it look like it has real geometry. Normal maps are like bump maps, as in the way they both trick the light, but normal maps actually change the surfaces normals and bend the light. Bump map renders faster but you do lose quality. Normal maps are used more in low poly games. Displacement maps, because of their longer render time, are mostly used on objects that need high level detail.