A bump map is similar to a displacement map but it does not have the same impact on the mesh.  Displacement maps can distort and change the mesh.  The Poser Manual does explain the difference between the two. 

Smith-Micro does have a tutorial/explanation on ambient occlusion, but, in a nutshell, ambient occlusion occur in areas where surfaces are in close contact creating realistic shadows in inner corners, crevices and crannies.  You can either add ambient occlusion through lights or material based nodes.  And it can be evaluated in IDL.